I theorize that reasonable size climate-generated rinks tend to be very rough (unless artificially surfaced) mostly because ice expands as it freezes. The ice has to buckle to accommodate the expansion.
A large lake can do better, in spots. Suppose you have a shallow area. The shallowest place freezes first, because cold diffuses to it from the air first. Then frozen area then expands outwards, without much resistance, because there is no ice around it.
If the frozen area touches a shore, it may buckle just near shore, because near shore ice is still nearest melting, and is softer, and because the main part of the sheet may simply move to accommodate near-shore expansion instead of buckling (though the second mechanism won't work if the ice sheet reaches opposite shores).
I intuitive believe you will often get rough ice within a few dozen feet of shore, but fairly smooth ice most other areas. Not practical for a small backyard rink, but good for parts of a big lake, at least in a cold enough climate.
After the surface freezes, the layers underneath start to freeze too. At any given depth, they should freeze first around the initial (shallow) areas too, because that is coldest, and the same process should continue at those levels.
Of course, in spots where the lake freezes all the way to the bottom (the very shallowest areas), the surface will be pushed upwards, and will be rough, and maybe have hills as well. Nonetheless, a big lake may have many smooth areas, where this hasn't happened.
It is my understanding that people frequently skate on The Great Lakes (of North America), so parts of them must freeze reasonably smooth.
There is an obvious problem with my theories: I know for a fact that people used to skate on the C&O canal, which is quite thin (1 or 2 dozen feet) most places. I'm not sure how such a narrow body could naturally freeze that smooth.
Perhaps outdoor ice skaters in small or thin places like the canal accept much rougher ice than those of us who are spoiled by artificially surfaced rinks are used to?