Twitter is 11 years old and has never made a profit even though it's been publicly traded for 4 years. It has 330M MAUs but its growth has stalled.

Pinterest is 7 years old, has close to 200M MAUs, and is still growing at a good enough pace for investors to justify this kind of valuation. Pinterest also excels in huge markets which you are probably not familiar with: recipes, weddings, fashion, and interior design.

Even though most people you know don't use it, there are still 200+ million people out there in other demographics that do use it. Probably a lot of them have never heard of Twitter :-D.

FWIW I think Twitter is undervalued as well.