in this example 'to' is part of a 'to-infinitive' ...it it not a preposition.
It is similar to constructions like,
She has a desire to learn, Failure to thrive is a serious diagnosis in an infant.
You can read more about 'to-infinitives' here: 'to'-infinitives
When 'to' is a preposition it isn't followed by the infinitive but by the ing-form of the verb, (a noun verb) e.g.
I'm looking forward to seeing you tomorrow. He admitted to lying to his parents.