This is just me, But sometimes I feel like all slot always give the mega multiplier win on user that using small so that high roller will encourage to play it.

There are also high rollers that win with a huge multiplier. That is one reason why Chip's vault often time becomes negative. Some huge roller hit a mega multiplier, and as a result, Chip's vault suffer.

Exactly, that's why they are called high rollers because anytime they bet it's gonna be huge then with big multiplier it can really deplete Chip's vault.
Slots as we all know is base on pure luck, doesn't matter how much you bet, if it's your lucky day then whether whales or just average players, you can hit it with mega multiplier.