You are exaggerating here. Roobet is a popular and reliable crypto gambling site for sure, but that doesn't automatically imply that they will sweep all the awards since they aren't perfect or anything and have their fair share of issues.
There is no perfect casino because every casino has its own plus and minus points depending on player's preferences so all the other nominees are also not perfect because of some reasons.
Their biggest issue is mandatory KYC while signing up which chased away many gamblers.
I guess it is no longer an issue in this crypto gambling industry since few years back when most licensed casino has to follow the regulation/rules from the license.
Also, I have never heard of some of the gambling sites that got nominated and many popular sites like Stake, Crypto.Games, Duelbits, Primedice, Rollbit etc are missing.
Looking at the information about this awards, casinos or any other related gambling sites (affiliate or provider or something else) need to register to the operator first the the team of the operator will do check/investigation to decide the registered parties are reliable enough to be nominee or not.
In this case the operator of the awards is the Affpapa iGaming, perhaps the casinos you mentioned above are not registering themselves to the operator, that's why we cant see them in the nomination list.
Correct me if I'm wrong about this procedure for the awards.