Message Template Token limitations
Welcome to StackExchange Grant!

In regular messages token for other "entities" such as memberships, contributions or event registrations are not available because each contact can have any number of them. 

For example, if a contact had two memberships or event registrations, CiviCRM would not know which data to "fill in" when sending the email.

This is why CiviCRM has several special functions such as event and membership reminders or thank you letters for contributions.