why does lennie wander into crooks room?

Lennie says that he is looking for George. This is probably the case. When Lennie lies, it is a lot more transparent. When George is not around Lennie also gets lonely. Crooks is alone so Lennie wants to talk. This seems reasonable and quite natural. In Steinbeck's world, however, loneliness and isolation is what is expected. This is especially true for guys like Lennie and Crooks. Both have a small talk, which gives a short bit of companionship to both of them.