Yea, you don't see them as often as other Mod 60 types, but they are out there.
For me, the appeal lies in the availability of the walnut stock available on the 990. Few Mod 60 types were offered with anything other than stained hardwood. The walnut models tend to be more desirable to the Marlin fanatics. To the average fellow looking for a nice .22, the overall condition, appearance and price probably matters more.
As a matter of fact, there is a difference in price value for the walnut version versus the laminated model:
Good $91 Excellent $132 NIB $163
Either way, its hard to argue fault with any Marlin .22. They are fine rifles for what they were intended to do.
Have fun with your 990.