Drywall is manageable and cheap, I agree. But it's more painful than it should be for something that _will_ require maintenance.
There are a lot of downsides though. You lose airsealing, if you don't have an airtight building envelope on the outside of the drywall. You lose fire resistance. You often lose aesthetics, although I've seen this done extremely tastefully. You lose childproofing, and run the risk of a kid electrocuting themselves or destroying your plumbing or dropping stuff in the wall. You impose constraints on what can go on the walls and where your furniture can go.
Given that drywall is pretty easy to cut and replace, most people figure it's just not worth the costs for something you do infrequently.
And for telecom / low voltage, you have a lot of freedom of how you do it.