going to echo every thing new rider said.. and add possibly a cracked rotor (it can happen in theory).. or a Bent rotor.. either of them will require a new/known good used replacement.
since I have never had my rotor off, I don't know the answer to this.. is the crank tapered at all, even to the order of a couple thousandths of an inch? if so, the taper on the crank or the taper on the rotor may be worn, in which case, you need to replace the bad part.
on the tapered question, also, if tapered, it could be possible for the bolt holding it to be slightly loose (not properly torqued) and allow a wobble.
AGAIN, I don't know if the crank is tapered, this I just a possible cause if it is.