memes

Yes. By convention based on old reasons though. When computer screens became common they were low resolution, and a whole genre of serif fonts were made to look good on screens and low-end printers. Good fonts, but adapted to look good in pixel grids. Microsoft made Georgia, Adobe had Utopia to serve the same need. A font like Centaur would just not survive on a screen. Sans serifs worked better, especially the ones with straight lines, Helvetica is easier than Optima on a screen. But now... phone screens and regular screens are good enough to display serifs, but now we are used to sans serifs online. But there's no real reason for them anymore.