No knockdowns? Why would they not have this?
Probably lacking animations for them. I mean, MWO was supposed to have those but they were disabled back in the alpha/beta and never re-added. Presumably all 'Mechs added afterwards lack animations, and given rescaling done etc., it is plausible older 'Mechs don't have suitable animations anymore either.
If there ain't no knockdowns, there's no need to make animations, and therefore money and devtime can be saved.
I'd rather have knockdowns... Really, it would be neat tactical tool. Would allow balancing some weapons as well, increase their impulse even though they're not stronger otherwise, or something like that.