Does "to" skipped in front of join?
No, "to" is not required before "join" in this case. If you want to emphasize the reason of something, you can put "to" in front of the verb, however, the "to" is already in front of the verb here, it is just the verb "do" instead of "join". Often when the preposition "to" or other prepositions are placed in front of the first verb in similar contexts, you don't need it in front of the next verb. Ex: All I wanted to say was I'm hungry.