Upgrading meant exchanging your old car for a new car of the same segment, or a new car of a higher segment and it was simpler few years ago than now.
These days thanks to cross-shopping among segments getting popular, people ditching ICEs for EVs as well as people who would do away with every other segment but buy an SUV or Crossover, we see people replacing their cars with others which shouldn’t really be called an upgrade.
However, there are also some cars which are really difficult to upgrade. Let us discuss some cars and the reasons why they are hard to upgrade.
1. Features in the highest trim level:
Back in 2010 when you bought a base model car, you were content with it. The higher trim only had some minor features and changes added to it. You decided to get the additional features installed aftermarket for cheap.
Unfortunately, that does not work these days. Base model cars are sparsely equipped than the higher variants which not only get all the fancy tech and gizmos, but also the important features. The higher trim has all the necessary safety features and mechanical changes (in some cases) too.
MG Hector | Style (lower)

MG Hector | Sharp (top-end)
A safety conscious customer would rather buy a different car of a lower segment which is better equipped and safer, although it means downgrading.
This means, if your existing car’s (a base trim) current model year has a base trim which is poorly equipped and the higher trims are out of your budget, then your existing car becomes one that is “difficult-to-upgrade” from.
2. Discontinued Cars, Discontinued Variants
a) Discontinued Cars: 
Some cars like the VW Jetta which are solidly built, luxurious, fun to drive etc. for these special cars, a replacement would only mean going into the BMW/Mercedes/Audi territory.
BS regulations (I mean Bharat Stage), brand shutting shop etc. are some causes which factor into a car being discontinued.
b) Discontinued variants
Baleno RS was one of the few hot-hatches in India. It gave you the power of 101 horses at just INR 8.76 Lakh (ex). The current model year Baleno is not a logical upgrade over it by any means.

Similarly, a new Endeavour over the old 3.2 seems more like a downgrade considering it is underpowered.
3) Entire Segments on the verge of extinction:
D Segment sedans — They are almost extinct with people moving to crossovers. As of now, the Indian customer is left with just 3 contenders: Civic, Octavia and Elantra.

When an existing Toyota Corolla owner would want to upgrade his Corolla (now discontinued), he would be left with the Octavia, Elantra and Civic. The only reason he chose a Corolla over the other D segment sedans then was Toyota’s reliability, and assuming he doesn’t want the Skoda due to its service bills, niggles etc; and the Elantra’s lack of diesel works against his requirement, the Honda Civic is a ‘take it or leave it’ for him. Believe me, even one model exiting the segment or one lesser choice makes huge difference to the buyer.
Those who appreciate D-Segment sedans would agree that it is not easy to replace in a time when the world is moving on to crossovers.
4. Enthusiast Cars:
Let me ask you to find me a replacement for the Octavia vRS.
I bet you wouldn’t suggest me anything less than a BMW 3 series. There aren’t many cars
specifically for enthusiasts in India, and even a Abarth Punto or the Palio 1.6 which was way ahead of its time. Enthusiasts
won’t find that fun on a budget in the current car scene, making these cars too, hard to upgrade from.
(By Enthusiast Cars, I do not mean only fast cars. Old cars which have an emotional connect to them have also been hard to replace for some of us. We enthusiasts would all agree that modern cars lack the feel and feedback that a older car gives.
Until the launch of the Thar 2020, there was no proper lifestyle 4x4 which would be a proper upgrade from a Jeep.)

The pickup truck scene in India currently has just the ISUZU DMax Vcross, which is specifically for enthusiasts. Who can suggest me a replacement for this? Now, that’s all the enthusiast cars I can think of. So let’s move over to the final and most common reason why some cars are hard to upgrade.
5. Simply overpriced cars:
The Innova in 2010 retailed for just about 10.xx lakh.
Now, 10 years later, it is about 10 lakh more expensive. So is the Fortuner. Likewise, other high-end cars are also heavily overpriced.
This, car, the Maruti Suzuki Wagon-R costed 3.6x lakhs then and costs just about a lakh more now, which is acceptable. This is why, the Maruti Suzuki Wagon-R is not a “difficult-to-upgrade” car while the Innova is.
The Bottomline: Most of the points in this post overlap because cars are more expensive and more advanced. Some of these cars are special because they are hard to find an upgrade to. Price (or your budget) factors the most into a car being hard to upgrade. Please add on your points to this list as to which cars are “difficult-to-upgrade” and why, and share with us if you owned a car which was difficult to upgrade.
What is the solution to these difficult-to-upgrade cars?
Answer: The Pre Worshipped Route! It is the only way to get a better car at a pocket-friendly price. You would get lots of variety and if you search hard enough, you will find the perfect car to replace your “Difficult-to-upgrade” car. If you haven’t already, Team-BHP’s amazing threads:
"Almost-New" used cars! The logic & beauty of buying 1 - 3 year old pre-worshipped cars and
The not-so-obvious advantages and
New car vs Used car are worth checking out.