This has been the arrangement in our parish for at least twenty years. I suspect the priests would rather be at the side, but there isn’t room. They have to move round the back when the Crib is there over Christmas, or the Easter Garden is set up, and it gives quite a different feel to the occasion.
Sitting at the front has several advantages. It means we all feel involved, as the celebrant is among us, and leads us in the Creed and so on, possibly making more people actually open their mouths and join in. It must have a certain sobering effect on any children or teens who might be inclined to misbehave. The priest can see if there is any hitch - for example, he can see the Offertory procession forming and if there’s any delay which affects when he stands up. And I know they take the opportunity to scan who’s there and if there’s something they need to follow up - Mrs. Jones not there, is she back in hospital, that sort of thing.
I’m quite sure they are not sitting there out of feelings of aggrandisement. It’s a really exposed position - imagine, feeling you are being inspected by so many pairs of eyes every time you change postion.