First, I'm unaware of the trend or situation of Alleman prior to 2020... but I know they were one of the loudest about their enrollment drastically changing once COVID rules were put in place. It seemed as though many didn't even bat an eye at taking the leap across state lines whether driven by politics or just simply so their child could play sports.
Assumption is 5.2 miles from Alleman's campus. I think that rules out the travel distance or cost concern. Alleman is not a diocesan school as far as I can tell with a quick search. I think this is just a big ball of things that's led to this.
I'll end with this... the WB6, for what I've payed attention to over the years, has a history of being quite stingy and arrogant in regards to their status, existence, and the members they have or take in. Alleman is an OG, so to speak. They have a history with the WB6 that is cherished by many. But I wouldn't be shocked if the WB6 decides to remove them after this season. Mainly, with the lines of sight we currently have, as it seems this will be a much longer or perhaps permanent process for Alleman.