So, I hope you've had enough sugarcoating and false reassurance from the previous posts. Because I'm about to slam you with some harsh reality.

The reason why others often leave your party is... Yourself. There is indeed a culture of leaving the party at the earliest opportunity without saying anything instead of addressing the underperforming player if you aren't satisfied. Whether you prefer this or not, this is the way many will act. Now, people often leave your party and there is a common element between all of them - you. A cursory glance at the couple of P1S kills you have tells me that you are indeed the underperforming player. You might do mechanics right but it is obvious you struggle pressing buttons while doing so.

If you are looking for genuine advice, start practicing the very basics - GCD uptime. Maybe even in less demanding content like Aglaia. Doing both mechanics and a somewhat competent rotation at the same time is the fundamental you are missing.