I think, the reason is, that every platform has wildly different games.
The PS4 only has PS4 EA games
XBO comes with XBO and 360 games (do also OG Xbox titles get released with the service?), making it's offering twice as large as on PS4.
PC has the whole EA PC history, including all the games from PC-only companies like Bullfrog, Maxis or Westwood they bought up. It probably has a range of at least about 3 times as many games as the other 2 combined due to this.
In other words, you'll get by far the most out of it on PC, and on PS4 it has the least value if it has the same pricetag across all platforms.
You'll get the least value by having to pay 3 subs for the same service.
duduspace11 "Well, since we are estimating costs, Pokemon Red/Blue did cost Nintendo about $50m to make back in 1996"
Mr Puggsly: "Hehe, I said good profit. You said big profit. Frankly, not losing money is what I meant by good. Don't get hung up on semantics"
Azzanation: "PS5 wouldn't sold out at launch without scalpers."