Subtitle are like 1h worth of content, why even download more than 10 a day?

They could make it 20 and it wouldn’t change much I guess, 10 does seem a bit low, but if they make it 1000/day (which you could argue is “no heavier than one JPEG”) they’ll have Kodi addons or whatever attempting to auto-download an entire library’s worth of subtitles. It’s not about the throughput, it’s about the processing time of establishing connections, negotiating cyphers, processing a request, hitting a search indexer, etc. All those small costs add up if every day you have thousands of users downloading hundreds of file without giving anything back.