The preposition "to" precedes the verb "reach" has not been used as a preposition. It's used as the sign of
infinitive.
The crucial point is that when "to" precedes a verb, it does not belong to the category (part of speech) 'preposition', but to the category 'subordinator'.
In modern grammar, we say its category is "subordinator" and its function is "marker". 'Preposition and subordinator are category labels, 'marker' is a function label.
ps: Some grammarians call infinitival to- a defective verb, but that's a very theoretical approach, and difficult to teach.
