When I started this game as very first MMO I didn't know what exactly to expect. My first few month I was leveling different classes, doing dungeons. I was in a social FC and people tried raids and they were lacking a tank so I (fearfully) agreed to jump in. I was neither a good tank nor did I know at all what to expect.
We got a weekly kill and so we did raid for 3 weeks to notice I lacked accuracy. To get the accuracy it was for me the simplest solution to replace my weapon and for that I needed to beat ex primals. So for the upcoming 2 weeks I jumped on every trainings and/or clear PF I could make up until I cleared and had my weapon.
So my motivation to raid? Progress, the feel to have achieved something before it got nerfed (do you know the true beauty of T7, A3S?), passing time with friends or people that gather together via PF and have the same goal and after all gear is also a factor even though only a small one for me.