It seems, bookmakers keen towards Topuria. I look at the comments and Topuria had higher odds, I think 1.91 will be the final odd or if they increase Volk's odds and decrease Topuria's odds, that will be a huge mental shock for Volk. It probably already is when it moves from 1.53 to 1.91 and you are getting anticipated. Many people even compare this fight to Aldo - McGregor.
I have no clue how do bookies set their odds, but I suspect they adjust them accordingly to how people are betting. So if public perception is that Volk is on the decline (because of the way he lost to Islam) and that Topuria is on the rise, and much more money was going on Topuria - then they might be forced to adjust the odds to mitigate the risk of making losses in case of Volk's losing.
Volkanovski is favorite to win but some people are saying he is too old to fight in same level with Topuria so he made great funny video for this, and you must watch it.
It is only two minutes long so you wont waste time, and he did a good job acting and making fun of himself, and I think he earned some money from casino for doing this:
https://youtu.be/C2nsn2uzWogThat's pretty funny. He's got a lot of distance to himself and probably one of the strongest mentalities in the sport.