They do, but in Europe the public transport infrastructure is more extensive, cheaper and more frequent. Hahn works for Ryanair as a ULCC, but YHM doesn't work very well for ULCCs in Canada due to the comparatively poor infrastructure. The population density and frequencies in Europe also allow secondary airports to thrive, whereas in Canada they are too low in comparison, so filling a 737 sized aircraft and having enough flights out of a secondary airport to support the necessary infrastructure and staffing (bearing in mind mostly shared contract workers) is problematic.

Hahn didn't even work for Ryanair during and after Covid as the frequencies dropped off and they established operations at Main, but they moved out of Main last year as traffic picked up again.

WS is also not a ULCC, but will still be an LCC requiring hub operations as opposed to point-to-point flying only, which is the mark of a ULCC. Codeshare and hubbing are a key part of WS operations to fill the aircraft, something that won't work in YHM due to the lack of partner airline presence. As mentioned before, airline planning and operations are not a one-dimensional problem, those who think they are are doomed to failure if they are trying to run an airline.