Noun + to + gerund

Because you are introduced to things and people identified by nouns, not by verbs.

You might be introduced to snails for example, or to Professor Mollusc the great expert on snails, or to research on snails, or to doing research on snails. However you would not be introduced to do research on snails unless you were being given a job with Professor Mollusc, in which case you would be introduced to Professor Mollusc in order to do research on snails.

You might also be introduced to track athletics or to running, but you would not be introduced 'to run' unless you were being introduced to the athletic club in order to run.

The use of the gerunds "doing" and "running" in these examples is because you are being introduced to them, so you need the verbs to act as nouns. That is they must be gerunds.