I personally think it's that football has become more and more athletic. An athlete with limited technical ability can impact/survive playing in a game, much more than a technician with limited athleticism. The game is as fast as it's ever been, but the standard is still very high, it's just played at a pace that makes it more difficult to highlight the technical aspects. With better coaching, s&c, nutrition etc. The standard of players is also much closer (still better on average) than it was in the past. You don't see an Henry running past someone at ease as much, because all of the players have a good level of pace.
The Premier league has more money than ever, and more teams are able to spend good money to bring in top players from other leagues. So the difference between the top and middle isn't as wide as it used to be, and that middle group can all beat each other, so it's becoming a lot more like the Championship has been for many years.
Recruitment is paramount these days and clubs like Brighton, Bournemouth, Brentford have been ahead of the middle pack in terms of bringing players in to the league. Everton spent good money last Summer, on a left back who never players, a wide player who rarely plays, and 2 midfielders who rarely play. Really for a club with more limited resource, the money needs to be spent on players who impact the first 11. I agree with bringing in players with sell on values etc. but if you don't play them, then it's a pointless exercise and wasted funds.