> I'm curious about how much work goes into recording high-quality, looping sounds like this?

When I started the site, I mainly used CC0 licensed sounds others had recorded.

Then I started recording my own sounds. How much work it is is very situational - if you regularly find yourself in an environment which has the sound you want to record, and not many other sounds around, then it's pretty trivial. For example, you want to record rain in the forest, and you regularly walk in a forest where it rains and there aren't many other noise sources (e.g. other people, planes overhead, singing birds, etc). The actual recording itself doesn't take much work, because I shoot for a level of sound quality that will satisfy 80%-90% of people, rather than a real "audiophile" quality level.

On the other hand, if you want to record something that only happens occasionally and with lots of other noise sources nearby, it can be a ton of work. For example, you want to record the sound of thunder, but you only get occasional storms, you live in a city with lots of other background noise, and it usually rains when it storms and you want rain on the recording. In that scenario, you might have to travel far and burn a ton of time trying to get the right conditions for recording.