Speed. Without the complexity of gearing.
They were racing machines, pure and simple. There's one in the Glasgow transport museum with aerodynamic rim profile and flattened fork blades! I think it's about 20-21lbs, still quite respectable today.
The smooth ride of large wheels on rough roads was a plus, but the larger the wheel you could turn given your inside leg measurement, the faster you went.
In the UK, gearing is still expressed as the diameter of the equivalent ungeared wheel - you'll turn a 100 inch gear going downhill...
Gears would add weight, noise, complexity. Belts, friction, slip, lost energy. Chains ... OK, when the Reynolds chain was invented, it took over.
But chain wasn't that revolutionary. All Reynolds added was a gap between rows of links, which could ride on sprockets (different sized sprockets, for speed multiplication).
That basic style of chain was centuries old by then, and in a form that blows the mind if you think about the implications of making it... that silver thread in the first photo is a chain, probably 0.2mm thick, with links about 0.5 by 1mm, assembled by hand. And repaired by hand too. (Yes, that huge planetary object is a 1c piece)
As a watch spring ran down, the chain transferred its pull to a larger diameter on the fusee cone, to keep the pull and the watches rate constant. If you think our engineering skills are that much better today, read it and weep.