To be fair, it's not just loamer mountain bike trails that are taking a beating. Numerous 'loamer' or semi-secret hiking lines in the Grouse Mountain area that use to see almost no traffic are getting completely blown out as well. As 'thaaad' said, there has been an extraordinary expansion of peoples free time in the last few months: a combination of people off work, schools closed and then none of the normal out of school / work activities, sports and social outlets available. All that has been left to do is spend time outside or inside on screens.
It did not help that BC parks, DNV and Metro closed so many trails and access points and kept them closed even after the evidence became pretty strong that the the risk of transmission outside is extremely low (with a few exceptions obviously). This only concentrated people in the remaining places that were somewhat easy to access.
The final thing that I believe lead to this was that people were doing their best to find places to ride (and hike) that were less busy in order to avoid close contact with others. Loamers were an ideal way to get away from the crowds on some of the more established trails and trailheads. This was exactly what we were all being asked to do when this all started so I don't think it was necessarily irresponsible behavior at all.
The big question is whether this explosion in mountain biking and hiking will die down as things gradually return to "normal" or if a lot of people will now have made it a new part of their daily routines. If that is the case, I hope our local governments are ready to quickly respond to this increased demand. However, based on past experience with DNV, Metro and BC Parks, I am not at all optimistic in their ability to respond quickly to anything positive in relation to mountain biking. As an outsider looking in, they all appear to have an antagonistic, passive aggressive response to anything mountain bike related, seemingly not realizing how main stream it has become or the significant impact it has on the local economy.