Cheap and frugal which shows a negative connotation and which shows a positive connotation? why?

Cheap is negative and Frugal is positive.

Cheap is negative because it is when somebody is afraid to spend money to have short-term savings and in the process they reduce the quality, value and time they have.

Frugal is positive because it is when someone prioritises their money and only spends on things they really need.

e.g someone cheap will buy lots of badly made chairs but a frugal person will buy one chair which will last longer.