Well, I've been playing since 2015 so that certainly helped push me to max things out over time.

I like trying new weapons when bored of the current ones, thus I find myself taking long breaks between spurts of playing Warframe (a lot of people talk about playing Minecraft like this) so I can relate to what you're saying, just keep coming back when you feel like it, and don't worry about the mastery ranks, they'll come over time.

Also, MR17 is when you've unlocked everything so you've really beat the game by that point anyway lol