My guess would be that ofc the prices are going down at the beginning of a new season due to, as said before here, managers try to get rid of lost weight, e.g. old players, high salaries or just players who doesn't fit their scheme.
Furthermore, the aquisition of new staff increases at the beginning of every new season, also managers are spending money on the arena update, which means overall less money is available and managers will get less money on the market for mediocre players.
Well trained players are still worth a lot but rare. The "buy a young player - 1on1 training - and sell" syndrome is still omnipresent.
My personal guess is, that we don't have to worry about those lower prices right now, once managers aquired their arena update and saved up some money again, prices will rise again. I think this is just a temporary state.
I am more concerned about the overall low quality of players on the market, which is really frustrating. I either have to have really deep pockets or a loooot of time to be able to bit on players at ridiculus times of the day. But that might be just me...
Cheers!