No Hobby Membership or Plaque

You did not received the plaque since you did not leveled up your hobby enthusiasm to max level.
Only after you got that to max level you will receive the plaque and have access to the secret lot 

maxwell812 Do you have any Mods that could be causing this? Does it happen to just one Sim or all Sims; do they receive the membership if you move them to another lot?

Some Mods, such as Lot Debugger, have an option to fix missing hobby memberships.

I figured out the issue. It turns out that the issue has to do with the lot that I have my sims on. I edited an apartment so I think that that is causing the hobby sims to not spawn in.

Whether the hobby Sims spawn or not, you should get a plaque after level 5 in a hobby. I have mods to prevent both hobby enthusiasm and stop the hobby visitors from coming and my Sims still get the plaques and access to hobby lots. As mate54 mentioned, the ffs debugger, also known as the batbox because of it's appearance, has an option to give your Sim missing plaques. It also has a lot of other helpful features and I definitely recommend it.