It kinda was, but they did this same rugpull and closed their free api way back before covid.

They do still claim:

"250,000+ Weather Stations

Weather Underground is a global community of people connecting data from environmental sensors like weather stations and air quality monitors "

I think it's a bit like FlightRadar24 - if you feed them your weather station (or ADBS receiver) data you get some level of free access but with non commercial use restrictions.

It's a reasonable tradeoff --- if I had a larger lot, and if there weren't already a bunch of stations in my neighborhood I'd gladly set one up.