Sorry, but I call it ********. External GPUs before were absolutely fine, the only issues being because Apple didn't want to release OpenGL drivers.
I think this has more to do with a marketing issue than anything. If they allow you to use an external GPU, it would be much easier to buy a mac Mini and a high-end 3D GPU card, as many people were doing. Now, your only option will be to purchase a model with a better 3D GPU that Apple releases.
External GPUs were fine before exactly because the drivers were there. But Apple Silicon Macs with Apple GPUs change the rules of the game.
For the first time ever, Apple offers streamlined high performance programming GPU capabilities abs programming model across all of its platforms. You have unified memory, which allows for pro workflows impossible until now. You have programmable GPU caches and TBDR guarantees. You have advanced texture compression (that desktop GPUs don’t support). Most of all, you have predictability. As a programmer with keen interest in GPUs, I can assure you, it’s a big deal. That why gaming consoles work. You know exactly how the hardware behaves and you have intimate control over it. Apple gives you all this on all their devices - from the TV to the Mac.
Now, eGPUs complicate this. They break the nice set of assumptions and guarantees that Apple has carefully lined up. They behave differently. They make things confusing for both the developer and the user. How would you explain to a user that their video rendering works slower on a high-end desktop GPU than on an integrated M1? How do you convince a game dev to program and test for a super rare case that a user might run an eGPU? An eGPU will definitely be faster in some cases - a lot of games, scientific computations on the FOU, some other niche cases. But overall, eGPU support will make the average user and developer experience worse, not better.
One thing we know with Apple - they dint target the niche use case. They try to target the majority. Just like with M1, that screwed over a very small subset of users that want to run multiple monitors or need more RAM on an entry level machine, I am fairly sure that Apple is more then ready to screw over an even smaller group of eGPU users - if this means improving the experience for the vast majority of the users.