gerunds - Why so many –ing nouns (present participles) do not take the definite article “the”?

For example we do not say:

I look forward to the seeing you, or in the doing so.

But sometimes we say:

In the beginning, in the fighting, the ruling, etc.

As such, is there any different rule concerning the –ing nouns or they should follow the same rules as the common nouns do?

Answer

'seeing' is not a noun there. It's a verb. And due to 'look forward...' pattern, it takes the verb in the form of '-ing'.

I look forward to see seeing you.

Does the question still stand?