there are pros and cons about enclosed chains
maintenance is still there , just cause you dont see it doesnt mean you can forget it...
people fold the bike and than slamm it into the trunk and than the chain may rub somewhere ....
dito the plastic chainguard cracks after it has been abused and somebody is yelling warranty replacement
oiled chains are not supposed to sling the crap all over the place, if that is the case one need to take apropiate oil, and much less of it.
chainging a flat becomes more and more difficult with an fully enclosed chainguard

its not available for pennies . ... a custom chaingurd would need a horrendeous expensive mold ( a mold that size would usually be done for several hunderthousands units.... we however talk about a couple thousands instead. the mold cost alone would add quite a chunk to the bike. Plus it would be a truly propierty item , which folks go off on all the time.

available more universal chaincovers have problems with larger than usual chainring diameters and shorter than usual chainstays ... most of them dont fit right

and the list goes on


still i like them too on the apropiate bike
Thor