Because it's marketing for audio......
No seriously, even if money were no object, the fact is, some guys would still want an all-in-one solution AVR that costs $5,000 for 3 reasons - sound quality, convenience, and most applications don't require as much power as some guys think.
There is nothing wrong with going either way - separates or AVR. It just depends on your application and preference.
Some guys think separates sound better because some separates may have better SNR or THD or more power output or simply because they are separates.
Other guys will disagree because they have owned both very high-end separates and mid-level AVR and they think any improvement is not night-and-day and nothing to brag about because they have much more impressive things to brag about in their lives than some $2K amps.