Because the M42 lenses are far cheaper (for some)
And I have a very nice set of M42 lenses:
200mm f3.5 Vivitar (a very fine optic)
400mm f6.3 (probably not a very good lens, but better than nothing)
Go not to the elves for counsel, for they will say both yes and no.
Lots of OM "T-mount" (M42) adapters on ebay for dirt nothing. Just make sure it is OM mount and not 4/3 mount. For some reason the eBay crowd keeps callinh the 4/3 mount OM 4/3.
I have 2 of them. One is actually a reversing ring that also has 42mm threads on the ID.
I did a search on ebay and found several for about $12-$15 bucks. I found this one mounted on a Macrotel 150mm f/4.5 Bellows Lens for a steal. If you ever plan on getting a m42 bellow unit this would come in handy.