Having shove replace an attack in part of an attack action would add another layer of menus to go through because once you select attack, you'd have to decide whether or not it was a shove or a normal attack for each attack in the action. This seems to be more trouble than it's worth for accuracy to the tabletop. And just having shove an Action doesn't feel right because that's not really how it functions on tabletop. Having it a bonus action is a decent compromise.
As to the distance, the BG3 shove does not truly knock people prone (there is an animation where they fall down, but the target immediately stands right back up, no prone condition applied.) If the tabletop rules were followed we're now looking at three layers of menus: Choose Attack - Shove or Attack? - Prone or 5ft? Again, doable, but irritating to do every time. Losing the functionality of the knock prone in exchange for what appears to be either a strength-based distance or else just a flat 10 ft distance....again fair compromise. (I have to go check this later...I'm suddenly not actually sure the shove distance is even 10 ft.)
We're also losing Grapple as an option....which again, the 5e variation of Grapple works pretty well, especially in combination with Shove (Shove Prone + Grapple is basically an armbar, they're now prone and have no speed with which to stand up), but in the computer game, I have a feeling it would be a bit irritating to deal with regularly.
So, losing the ability to shove multiple times in a round (one for each Attack), the ability to knock prone, and the ability to grapple, in exchange for shove 10ft as a bonus action feels fine. And it's not like this is going to make Pushing Attack, Repelling Blast, or Open Hand Monk less powerful....those powers allow you to do damage in addition to adding the shove...and Repelling Blast lets you do it at range.
So, I'm good with their alterations on shove. It's not quite the way my shove-happy table-top group does things, but we already have proven ourselves able to find cliffs, stairwells, bridges, and lava flows to shove people off of or into just fine. The compromise here is close to that.