like switching from Walmart to 15 other stores just to buy the same stuff

As the other commenter pointed out: you do that once. And if you do it properly, nobody will be sending anything to a gmail address you don’t use anymore.
Then you have 15 stores all around the same parking lot, to stick with your analogy.

And yes, it’s always a trade-off with convenience, but much less so than you make it sound.