It's a problem inherent to all tournament structures: they are a meta-game with different rules and priorities than the game itself. Trying to win the tournament game (Arena season) is not the same as trying to win the game itself (see Barbados purposely scoring an own goal against Grenada in order to win a tournament:
https://www.youtube.com/watch?v=pmDuoZQINHI).
We're all board gamers here, if there's a way squeeze out a slight advantage we're going to find it. If you are playing the tournament game over the actual game you'll red thumb players if it gives you an advantage because it's allowed by the rules. The 'top' players in most Arenas are in over a dozen games at a time. I have to imagine that impacts the quality of their play, but prioritizing the tournament game means quantity is more important than quality. I have been able to beat top ranked players in arena, but I'm only playing 1 game at a time, making it easier to plan ahead and remember small specifics of this game to squeeze out some advantage versus someone who's in 15 games at once.
If you disallow red thumbs in Arena then you are saying the tournament game is more important than the actual game, because you are interfering with the integrity of the actual game (allowing players to avoid opponents who are taking technically legal moves but stalling the game in order to delay the loss hitting their arena ranking) in order to preserve the integrity of the tournament game (not allowing players to avoid people who can beat them).
There is an argument for this: If you don't want to play the tournament game why are you in Arena? Just play at regular tables. Personally I like the slightly more competitive atmosphere because players are less likely to time out (in the past I have found Beyond the Sun almost unplayable outside of Arena because I was constantly being matched with players who couldn't keep up with their timer even at 1 move / day), and more likely to understand at least the basic strategy of the game (I've played Evolution against players who have created a body size 1 Carnivore with no additional traits. If you know anything about how to play Evolution you know it is impossible for this creature to eat anything and it can only starve to death at the end of the round. I've seen a player do this twice in the same game).
Back to the original post: if someone playing the tournament game believes they can gain an advantage by idling in the game queue and then not accepting the game, because it prevents other players from starting games and gaining points, they will do that. I'm not saying that's actually what's happening here, it is more likely the case that if queues are 10 minutes long the player has simply forgotten, gotten distracted, or temporarily stepped away. Either way this does impact both the integrity of the tournament game and the actual game by preventing games from being started, so I agree that measures should be put in place to prevent it if it is a common occurrence. Either some penalty if a player is repeatedly missing the start of a game in a short time period, or a way for players to avoid users that are routinely doing it.