Because that would only work for those that have an active ESTA/Valid visa for US entry. You could offer, but a big nightmare in case someone misunderstands, says yes and ends up in the US without proper documentation.

I'm not aware of how it went down at the airport today (I'm only flying on Monday out of BRU and will monitor now), but my immediate guess would be train to AMS + KL flight for YYZ/YUL. FRA is too long and too complex by train (2/3 transfers and 3.30h+), CDG's last departure to YUL/YYZ is at 2PM, which would have been too close a call for an event happening at 10AM. LHR is also 2 transfers away from BRU by train and takes longer to get to by car than FRA.

So, given the crunch they must have been in, I think a taxi ride to FRA may make sense for the premium pax ^^, especially as I expect some (like myself) to connect to western Canada flights which are also served direct from FRA.

I don't envy the concierge team at BRU for 2 events in 2 weeks (AC833 was cancelled on May 14)...