The difference between 'attach to' and 'tie to'...
The title:

The main theory is that we like colors that are ___ to things that are healthy and promote survival.

A. attached to; B. tied to

I looked up the dictionary, and found out both of these two phrases have the same meaning in some extent.

attach to: to be connected with sb/sth
tie to: to connect or link sb/sth closely with sb/sth else.

I'm confused, the answer is B. It seems that A is okay.

Thanks if you are willing to explain.

Question

The difference between 'attach to' and 'tie to'...
The title:

The main theory is  that we like colors that are ___ to things that are healthy and promote survival.

A. attached to; B. tied to

I looked up the dictionary, and found out both of these two phrases have the same meaning in some extent.

attach to: to be connected with sb/sth
tie to: to connect or link sb/sth closely with sb/sth else.

I'm confused, the answer is B. It seems that A is okay.

Thanks if you are willing to explain.

Answer

In this context, "to be tied to" means "to be an important and inseparable aspect of an object". "To be attached to" does not have this second meaning.

That is, "tbtt" speaks of a trait of an object, and "tbta" speaks of two objects connected together. Since colors can be traits of edible objects but they cannot be attached to edible objects except through artificial manners like paint (which we obviously wouldn't have had in the several million years leading up to our species' current form), B is the better answer here.