Again, how is that different from packs of baseball cards?
There are usually no unprinted, weightless, white cards in the pack - all of them have a minimum value and market price. By investing a lot of effort you are able to select, collect and score rare ones with higher value. Effort does directly influence the outcome.
Now the problem is that a single game has a single manufacturer who appoints a value to the white, weightless, unprinted card and is therefore defining the market price/value of something that could be seen like currency and took him practically no effort to copy. He is the only place where you can spend the money, there is usually no free market for it. It would be like printing money in their own created market.
And even baseball cards can be seen as an asset and relevant for tax or debt. They are in many ways similar, but at least a physical good.
MMOs are usually highly addiction focused, with a certain pace in which lifts happen as long as you put effort in.
People like lifts, people can buy lifts or premium content in these games with real money (also no effort to copy there), but selling random rewards for money makes it unregulated gambling. I struggle a bit to see differences to raffles, but well... there you have a limited amount of lots and raffle prizes per draw so anyone can calculate his chances before purchasing a lot. Even basic gambling machines need a certain payout rate to be legal here, next to age restrictions and a permit to operate them. Gambling addictions are hard, btw.
EU law was changed in this regard recently as well, the MMOs i know then just declared what rewards are guaranteed when purchasing such packs (same value as for the usual premium content), added random extra prizes and the problem was solved. You were getting a guaranteed service for the price, not worthless items or promises without a given lots/prize ratio. Btw. i occasionally pay some money in such games, not to buy an item, but to extend a service contract ("virtual goods"), therefore keep their business running and can play the otherwise free2play game in the next few years. If i don´t play it, i don´t pay for it.
I approach such questions usually as: if it was no problem, i can not be affected by it being regulated. In other cases it probably is a problem to me or someone else and needs regulation.