Your immune system can and will adapt faster to something similar to something it's been primed to identify. A spike MAB that encounters a variant may be useless, as has already been seen in the southwest US..

https://endpts.com/lillys-covid-19-drug-bamla...a-variant/

These MABs have an expiration date and there's no telling when it will be until it's too late.

Now consider that treatment with spike MABs may interfere with the body's development of immunity as well..