You have to try to see things from the perspective of the producer and/or engineer - they're producing songs, not just bass lines. This is why they're called "producers". Their task is to take abstract vision - "the melody is upbeat, while lyrics have a darker undertone", "we want to retain some of the grit and energy of the demo, but more polished", etc. - and execute all the concrete steps needed to make the end product. AND this needs to be done within the constraints of money and/or time. Even if you've got a Beyonce budget, you're managing every minute because you've got a release date target to hit, plus you've got other projects scheduled, etc.
Also realize that all music is massively self-referential. Even when something comes along that's new and different, a careful analysis almost always shows that the novelty is more about an unusual combination of elements from the past. Knowing how to create various familiar elements precisely and efficiently equals a producer with a very full work calendar.
So..... you're a producer. Unless the song is going to prominently feature a very specific bass sound, you just need something that you know will serve the overall sound well. It helps a lot if you've got a bass sound that is flexible and that you are familiar with - i.e. you know that if you find in mixing that a deeper, dubbier sound would be nice, you can boost at, say, ~220hz with a medium Q - you don't have to go searching for tones. Which is good, 'cause you've still got 23 other tracks on this song to dial in, and 6 more songs in this project, and the release date coincides with the world tour announcement....................
So yeah, these guys often want a P bass. A lot of times, they even want a specific P bass that they've recorded before. Not because they think it's the alpha and omega of ultimate bass tone, but because they know it will work, because they know exactly how to make it work even if there's a fairly drastic change in vision during mixing a month down the road.
