A step up

Yup. That’s meant to be a dude riding the tarrasque.

Some versions of D&D have had a hard level cap (such as 4e) while others have unlimited advancement. While being forced to end a campaign is sad, having a natural end point is a handy narrative tool. At the same time, having an expected end makes people expect that the story will go all the way to the end cap. And not every story needs to continue. The longer you go the greater the risk of having the game devolve into silliness or absurdity. There’s a very fine line between Epic and Camp. It’s a little too easy for a DM to stack too much awesome onto their characters and devolve them into¬†caricatures.