It's just done as a precautionary treatment. Even if they aren't showing "signs" in particular, they could still be infected, especially if a fecal hasn't been done yet.

Dewormer will NOT hurt an animal, especially pyrantel(it's even given to people EVERYWHERE to get rid of pinworms). Ivermectin, on the other hand, if overdosed isn't a fun thing to deal with. Praziquantel is very safe too and can be found OTC now.

If you can get the meds at a cheaper rate and you can get them easier by yourself, why not? It's for the protection of your collection. Tapeworms can lead to regurgitation as we've already seen, wasting(massive weight loss), anorexia, and ultimately death. It takes longer for the bigger snakes to show signs as there is more bulk to them. The smaller snakes waste away quickly. Also, if a roundworm infestation is big enough, the animal can even start regurgitating the actual worms because they are backing up into the stomach and esophagus from the intestines. Not a fun thing either. Roundworms also have a migratory phase in which they can go through organs such as the lungs and liver, causing alot of damage along the way.

That is why I said, if one or two have it, regardless of the quarantine procedures, then treat them all. It's not going to hurt the animals at all, and if they do happen to come into contact with infected feces or equipment, then they will be protected(at least for a little while).