They can't cap it at a set $ amount because that would mean you would get a lower RTP the higher you bet, that would definitely be unfair.
Of course noone knows the actual RTP of the slots but most likely the win cap is factored in, I'm sure they can remove the cap but they would also have to change the payouts or make the big hits less frequent.
If players look at the second rule page, you will find this 50,000 x line bet max award on every game.
I suppose it doesn't matter much to those who wager higher, because you can get a bigger payout the more you wager, but are still capped at 50,000x your bet.
For the 1 or 2 cent player though, it is very dissapointing, especially considering the potential behind offering an expanding wilds game or increased line games.
This rule however doesn't just apply to features, it applies to all spins. But getting it during a re-spin feature, is really a dissapointment, since all 4 re-spins count as one spin. So if you are playing at 50 cents and hit a couple hudred on your first 3 re-spins and then on one re-spin hit the expanding wilds, you will only be paid $1,000, not $1,200 for all spins, because the 50,000x line bet is the max award for a single spin.
But as one poster pointed out, if you play only 5 lines at 5 cents per line, still playing 25 cents, the payout then would have been $2,500.
Most players are more comfortable playing with all lines covered, just as I was. I tried the 5 line wagering and found that my wins I did get were better, but seeing the wins I was missing gave me cold feet for playing this way.
So playing it safe and covering all lines, you risk not getting the full win we all hope for, playing it at the 5 lines can cost you a lot of wins you could have had, making this playing style hard to get used to.
Even if nothing can come of this, I at least hope to make more players aware of this RTG rule, so that when they one day hit a win like this maybe they won't be as dissapointed.