Why are the two related? Didn't Freemasonry come along several centuries after the Templars were disbanded?

They aren't.....

I understand that they aren't but why are they perceived so by some? What is the supposed tie in?

The supposed connection is that they are both 'secret societies' that are currently engaged in step 1,204,632,456,678,567,246,567,889 of their 3,234,565,678,324,565,556,787,345,356,982 step plan to world domination

What it comes down to is that if you want to be the subject of conspiracy theories, just refuse to tell anyone what you are doing, immediately people will assume that 'you must have something to hide' and start constructing elaborate conspiracy theories about you.

But some people aren't happy coming up with ONE conspiracy theory, they want to create a Grand Unified Theory to unite ALL conspiracy theories, and that's why people try to connect the Templars and the Masons, even though there is ZERO actual links between them.

I think the Masons may promote that alleged connection themselves.

That's what they want you to think

The Cat and the Tin Foil Hat by wally glenn, on Flickr

They just named one of their ranks or "degrees" as Knights Templar….

I have met some that, do actually think there is a connection.
Something about Scotland and some other strange events that don't seem to appear in any history text book I have heard of.

There are genuine successors to the Templar order. The Portugese Order of Christ, for one and the corresponding Papal Order for another. The disbanded English branch of the Templars was amalgamated with the Knights Hospitaller. The Freemasons claim to succeed to the legacy of the Templars is of a piece with their claim to succeed to just about any organisation at any time that had a fancy uniform or claimed some sort of "secret". The Masons do have a side order open only to Christians that calls itself the Templars but that's a 19th century invention. I suspect the Christians they recruit aren't very fastidious about the first commandment.