It's a one time cost. The others are monthly costs. Most likely they're paying for a redistributable licence which is much more expensive than other licences.

For instance, take a look at this font I'm currently integrating into the app I'm working on:

https://www.myfonts.com/fonts/intelligent-foundry/averta/ https://www.myfonts.com/fonts/intelligent-foundry/averta/buy...

If you want to put these on the web, you're paying $200 per font type. If you want to buy the whole family, that's almost $1200.

Companies with a design focus are happy to pay this in order to differentiate themselves from others.