That may be true but in an industry that produces millions of new computers every year there's quite a bit of room for outliers. After all someone has been buying all these specialised expansion cards for all these years.

Graphics, sound and networking may have been the biggest reasons and may now be adequately catered for in everyday PCs without the extra hardware. However the high end of all of those markets still needs more than what you get on any basic motherboard and processor and then there are all the speciality cards as well catering for who knows how many niche markets.

No, we're all doing that now. This loss of PCIE expansion is really annoying and I'll probably be skipping this next gen largely for that reason. Highend threadripper is unobtanium and has been for the last couple years. But I have a gpu from like every generation that I wish I could plug into my pcie bus and have it be useful, if I could buy a platform that supported that I would.

I have a PCIe sound card but I have to say these days that I'm actually using a tiny apple usb dongle for my audio, and it sounds cleaner than the internal sound card does. The dongle was also a fraction of the price of the sound card, and way more convenient.