I think it's a little more complicated than just having the proper quarantine steps available for algae on their site, as far as the brand is concerned, for various reasons.
If you provide QT instructions, someone claims to follow it, and the algae dies then they may expect a replacement claiming "your QT guidelines killed my algae." It's just one more excuse to give people. On here it's helpful advice, but on their website is a different story.
Then there's the more important reason. If you provide QT instructions than it indirectly suggests that the clean algae should be QT'd and isn't really as clean as the claim, though the big disclaimer achieves that same result.
Maybe stating all of the procedures that they go through (without giving away inhouse techniques) to explain how and why the algae is clean would give people a better understanding? Something like, "what makes our clean algae, clean." Then possibly follow up with something saying that if the person still feels the need to QT anything they put in their tank, here are some possible steps you can take? So it's not giving the impression you need to QT, but explaining the rigorous process involved on their end and the extra cost involved to the customer.
It's a tricky situation with how that's worded. I get the disclaimer is "legal stuff," but that disclaimer also implies that the algae isn't really clean. I would definitely make that disclaimer fine print, lol.
I totally understand your thought on giving people quarantine info as being a helpful thing. It may just subconsciously suggest to people that it's necessary and than what's the difference between this clean algae and eBay algae if they both need to be quarantined.