Typically its because the GPO configuration has 15 years of kludge and your IT department is under resourced and doesn't have the ability to spend 6 months sifting through and testing all of it.
In Windows environments group policy is often one of the biggest piles of technical debt.
But a big problem is how cult-like certain GPO setups have become. Asking my IT Department casually, 90% of the worst GPO settings we enforce at my current job are "mandated" in the agreements and contracts with a certain, supposedly prophetic (but unarguably profiteer) vendor of over-priced databases and accounting software "to keep their software working as intended". (Which may be quite accurate if their software is truly intended for the slow torture they provide from a user's perspective.)
That's a great bumper sticker.
There are so many cases you find of people's Windows complaints where the questions are "Why does Windows even allow GPO to hurt users that badly?" and "Why does your IT staff hate you so much personally that they configured Windows into that particular contortion?"
The Unix world has decades of tales of the "sysadmin from hell" / BOFH, of course, but something about Windows administration just seems to elevate to almost universal "art form" across every company, but at the same time has managed to make it "business as usual" rule rather than the to-be-irked-by exception. On no other operating system would that level of IT micromanagement and terrible "security products" be accepted, and on just about no other platform would people just as easily assume it to be OS "bugs" or "inabilities" rather than the forced masochism of some local BOFH.