why use ATP as an intermediate instead of coupling reactions directly?

Glucose isn't a very reactive molecule so it isn't useful to use it directly.

Glucose cannot be broken down completely to release its chemical potential energy in a single step. It would therefore take too long to obtain the energy.

If glucose's chemical potential energy could be released in one go too much energy would be released. The excess energy that cannot be used would be converted to heat and the amount of heat would destroy the cells.

ATP releases energy in a single step so makes energy available immediately.

The amount of energy released by ATP is a small quantity of energy that doesn't release a lot of heat.

Because enzymes involved in other things just don't have taking-apart-glucose functionality.
Taking apart glucose is a big undertaking.
Popping a phosphate off ATP is much more portable.