Though rather obscure, there is even an official term for two Transformers in a relationship: "sparkmates".
Perhaps there is no reason for them to engage in romance, but then there is equally no reason for them not to.
Regardless of opinions, Transformers engaging in or pursuing interaction of a romantic nature is a well-established element in pretty much every continuity.
For the most part, Transformers are observed searching for romantic partners amongst their own kind, but attraction to organic lifeforms and even non-living objects has been documented as well.
Some wonder why a species that likely does not reproduce sexually would participate in behavior that in other creatures exists as a means to promote sex and thereby new life.
While a definitive answer to this has yet to be given, the question as to why Transformers become romantically involved with one another can be approached from a different angle. This is shown through their very human-like society, interpersonal interactions, familial relationships, and even the fairly common practice of merging bodies and minds.