While the House puts some limits on debates, to move things along, the Senate is a more deliberative body (by design) and therefore doesn't vote on an issue until it has been completely debated. There is no strict definition of "completely debated" beyond "someone still has something to say." As any half-awake hacker no doubt will notice, this means that you can prevent a law from getting voted on, and therefore passing, by simply not ending the debate. This is what a filibuster is.

There are technically some restrictions around debate, and the band-aid fix that a supermajority vote can stop debate and bring a vote, but that's about the only thing stopping it in practice.

The main technical restriction is that, if the Senate doesn't have anything else to do, any one Senator only gets one monologue. They can't stop one day, and then filibuster again the next day. This rule can be stretched, but not broken. Hence, the content of most filibusters tend to be long space-fillers, which is what you're seeing. There's also a rule that the debate must be 'on topic,' but that's too vaguely defined to be worth anything. Famously, one Senator said something to the effect of "this law is not in the interests of my constituents, who are as follows:" and then proceed to literally read the phone book for a few hours.