I assume it is because education churns out people that think it is a job and not a calling, ie they do not care to much. They just do a minimum of things they have to, why learn the more difficult things when you can just whip up something i VB for Fortune 500 and earn more?
In the older days, you where interested in the field, today it seems like more people are into the field due to it can be a well paid field to be in.
There's still many people going through the system that do care and programming is their life. So those people are still making it through the system.
However, demand for programmers far exceeds the supply of those people, thus lower tier (like anything below say MIT, Carnegie Mellon, Cal Tech, etc.) colleges are constantly lowering the bar of entry for their CS programs in order to draw in enough student bodies to fill expansion in those programs to meet the demand. It really was a really shocking to me to meet some of the fellow CS students of one of the kids of one of my cousins. But that's not surprising as there was a study done a few years ago showing that programming is a field where you not only need to have a desire for programming but your brain needs to be capable of understanding programming logic and complex algorithms. And no matter how much time is spent attempting to teach someone without an "affinity" for programming they'll never progress beyond relative basic programming ability. IE - most people could learn to do advanced math with time, most can't learn to become a good programmer.
It's also harder now for a student to have a really broad technical base for CS due to the extremely limited number of elective credits available due to mandatory non-core credits required (the basics such as english, foreign language, history, art and non-core sciences as well as newer requirements for social and gender programs). When I went through university about 1/3 to 1/2 of my credit load could be dedicated to electives of my choice. Nowadays that is down to maybe 1/10th (or less depending on the college/university) of a typical 4 year degree credit load.
So, for example it's extremely difficult to take a core CS focus and then have a broader understanding of alternative CS focuses or even math and science. IE - due to the non-core requirements being greatly expanded at the expense of elective credits, it's almost impossible for a student in college/university to have as broad an understanding of the field and related fields as in the past just due to the inability to fit it all within their 4 year degree. And going for a Master's degree doesn't help with that since a Master's degree just focuses you even more on a narrower focus.
On top of that, non-gaming companies are able to offer significantly more money to attract top talent coming out of University. Due to the boom in AI, companies like Google, Amazon and Microsoft are getting close to offering a million USD a year to experienced AI programmers, that means the bottom end of the stack (programmers coming out of university) are likely also getting a huge bump in what they are being offered.
That means that for the people you are referencing, gaming is being relegated down to the level of webdev in terms of financial compensation when compared to what the big tech companies are offering for top talent.
IE - it's all a combination of the really smart guys from before retiring and the remaining really smart guys increasingly being drawn to opportunities that pay more. So, people that would have gone into engine (rendering) development are instead looking at what the big tech companies are offering and choosing to go that direction instead.
There's not much that game developers can do to attract that talent, especially when they are limited by how much they can charge for games.
The only companies that might be able to afford to offer something vaguely comparable to what the big tech companies are offering are dedicated engine devs ... like Epic. That means that all the best engine developers will eventually migrate out of development houses and towards dedicated engine development houses (Epic, Unity, etc.).
Due to the economics involved and limitations placed on game developers WRT budgeting, it's just not possible for most AAA game development houses to support a dedicated engine developer, much less multiple in the same as they could even 10 years ago. It's far easier to have someone that can modify an established engine's rendering code and leverage resources that can be shared across multiple development houses.
When so much of AAA game development relies on graphics and graphics assets. Do you pay 1 guy multiple hundreds of thousands of dollars or do you hire say 10 or 20 asset design artists for the same amount of money?
Regards,
SB