If a casino wants to hold 8% of the handle, well, it damn well better do that, since that is what they paid for the software to do.
The whole idea is that the reels and paytable already are calculated to give the casino their house edge.
To do it easy, you can imagine a slot machine with only one reel and it costs 1$/spin.
The reel has only 10 symbols which are numbers from 1 to 10, and here is the paytable:
1 = 1$
2 = 2$
3 = 3$
4 = 1$
5 = 1$
6 = 1$
7 = 0$
8 = 0$
9 = 0$
10=0$
The RTP is 90%
To do this with 5 reels and a lot of symbols with wilds and bonus games etc you can with a lot of maths combine it to a paytable with 95% rtp.
This is why casinos can adjust the rtp with adding/reducing symbols on reels.
The most known one is the additional pear on reel two on the RTG slot Fruit Frenzy.
From the very first time you make a deposit and lose, you have begun a cycle that works in the casino's favor, for most people.
The most common believe by players who notices changes in how the slots are behaving is that there is a cycle.
It's wrong. There is no cycle.
If it was a cycle, experienced players could easily figure out when to raisen the bet size.
With the software it's much easier for the to use other methods
if they want to adjust/stabilize(call it want you want)

the RTP.
All big casino softwares have a tested random number generator(RNG). Every time you click spin it produces a random number.
If we use the easy one reel machine I mentioned it can easily be tampered with to be either paying out more or less like this:
1. The machine has been paying to much lately, then when the RNG gives the machine the number 2 it's not approved and the RNG produces a new number, 4. Bingo, an approved number which is not paying out more than the bet.
2. The machine has payed out to less lately, then when the RNG produces a losing number the machine is not approve it and the RNG produces another number.
This was only an example and don't forget that the easiest way to cheat players is by todays crappy bonuses. To make players deposit and have a playthrough which is nearly impossible to make they have earned more money than the house edge