I wonder if it's the case that it'd take more effort on the developer/company side to design more streamlined updatable software and they wouldn't see the direct benefit?

So they're not as bothered, given that it's the user's time spent waiting for an update to be applied, rather than their time spent coding a better way of delivering updates.

Related though, I always find I'm more willing to spend time updating if I know it's making an improvement or adds functionality. I like getting a new feature to play with. Maybe always having a recognisable new feature as part of an update so you're more willing to put in the time to do it is something. Use the carrot rather than the stick...