That may well be, but this is an intentional descision. Fully integrated HiFi solutions are typically targeting entry-level HiFi customers but that isn't for technical reasons. The typical audiophile customer has been brainwashed into the thinking of seperate units for everything being technically superior, plus it gives room for the customer to play and make a hobby out of it, following the constant path of upgrading and replacing subunits and talking about it in forums ;-)
I agree that it is not likely to be technical decisions but intentional decisions to keep the price down to sell for less.
IMO it's also harder (& more expensive to design a one box fits all with out the very low internal signals signals interfering with each other due to internal proximity.
I believe that to get the same quality as separates, it's going to cost more to accomplish due to the small signals involved internally & their proximity to each other & the larger amplifier signals. Of course, others may have other opinions.
For me, personally, separates have an ease of replacing a single unit item that has failed with another, In my case, I have a replacement for each item in my chain of gear on hand & can simply swap out any piece that has in some way failed with another. I never thought of all in one as being an advantage. Not even since before I was into audio (enamored by it at age 14, started actively in it at age 17 [1974]).
Here is an example: In other gear for other purposes (lawncare): I have a dedicated weed whacker and a separate edger (2 of each, 2 chainsaws (+ a mini one), a 50" rider mower, a 30" self propelled more and a 21" push mower. And a backpack blower (the only item that I don't have a backup for [but I can manually rake the leaves & use a mower to blow off the sidewalks]).
None of this is for Professional use, It's simply to make sure that I can get my 90 year old mother's 3/4 of an acre & my 1/4 of an acre (we live 12 miles apart & I keep the gear in a shed at my house & trailer it back & forth) done whether what I am using decides to run or not. It doesn't matter, no drama, I have a backup tool to use.
If I own something that I like, I buy a second one (because it may not be being made in the future). Shirts, shoes, etc.
To many, this seems odd: to all: you live your life your way and I'll live mine my way.
I learned this having 2 of everything (I was already doing it haphazardly but this person really made the point to me & I started doing it in earnest) Jeff Dorgay the founder of Tone Audio Magazine (One of the most subjective oriented magazines that I have ever read). But this idea has caused my life to have much less drama. And much less things disposed of.
Due to having the time to find great people to repair something without needing to immediately find something else to replace it. YMMV.