Generally the problem is not that ETF2L doesn't want to allow new maps to be tried, but more about people always preferring to play the same maps over and over again. Right now we have been holding cups before every season in the past 2 years (except for S28). And to get a proper result from all of those, we always have been gathering information from the top teams on how did they feel about a certain map played in a cup and a certain map played in the season before.
Now sadly, more often than not the results from that have received have shown to us of people wanting the same 6/7 maps being kept every season, while the newer maps just barely wouldn't get in, even if we would prefer the votes of top players who did take part in said test cups. At this point making a decision gets way too hard, it's not a simple thing of just removing a map and adding another one in, since it really does have impact on the season after that too and numerous other European events that we simply don't want to fuck over just because we aren't running some specific map in the map pool anymore for the current season.
Realistically we would still want to give new maps a try whenever they do deserve it, but knowing that the main map pool that ETF2L has contains 5 maps that everyone likes and 2 that could be considered to be replaced, which doesn't leave too much room in the end for a single map to be enough good in this part of TF2's age to be accepted in the competitive map pool when we all are aware of the base maps already so well that they have gotten in to the game officially even as well. You never know however when some new (or even an old) map would surprise and blow others out of the water though, but I'll be waiting for that day to come when the feedback given is always very minor and not really helpful to the mappers, like how you can see it from this thread alone even.