They have added features though. They're just not invasive. They added masked emails, for example. And if I look at the settings right now, I notice they've added customization of what swipes do.
I too like the feeling that they're stable. I guess they're just tactful with their additions.
I switched a couple years ago because the masked emails and i was tired of histing anonaddy and i couldnt be happier myself. Easily the best mail provider i have used and i have used a bunch of them (including all the big guys, a provider using zimbra,protonmail, etc)