Another way of pointing to the same concept is how a chain as a whole is a resilient thing, but this is because each link has enough give to absorb strain. So a system is made durable not by its components being unbreakable, but by ensuring that individual parts can bend/fail/adapt. A society can hence be enduring only if its parts can be sacrificed for the whole. If a single specific part is worth you more than anything else, the system/society may be traded away for it.
(I think this thought is from Nassim Taleb, but I am paraphrasing a lot and cannot pinpoint the exact source, likely it is Antifragile)
I am myself thoroughly confused on this point (and for what its worth, a lot of our experience seem to overlap), but I can provide some competing hypotheses:
Some kind of a selection effect: Banter is not the cause of sex, but is a way to discover whether the other person is open for a hook-up. People not into casual sex (either generally or at that particular instance or with the particular person) will produce different responses.
People with similar reference points will recognize each other and the mutual intent and escalate via physicality or discussing logistics/intent openly.
It allows non-interested people to be selected out covertly. This is an important feature as it seems some people feel violated if they receive a (semi) direct inquiry about being interested in hooking up.
Due to different cultures/expectations, people often misidentify the response (typical mind fallacy), which downstream causes things like accidental harassment and the “OMG, I just realized 2 years ago that girls wanted to sleep with me”.
It may be an alternative way to increase the hornyness of the other person if physicality such as dance is not an option.
Whatever the solution is, the effect may be highly (sub)culture dependent. This is compatible with #1, the point being that your local culture may have specific procedure and signs that are very reliable, but in different groups they may lead you astray. For example, if you have a lot of prior experience showing that hours of banter in a generic college study group does not get you laid, but two minutes of chit-chat in a Fetish party does, you will be thoroughly confused and will not escalate when the latter happens again, as in your experience that is just not how it works.