פירוש על קידושין 68:4

The fact that women are exempt from tefillin led the rabbis to derive the general rule that they are always exempt from positive time-bound commandments. But instead of deriving the general rule from tefillin, why not derive it from the mitzvah to rejoice on the festival, a positive time-bound commandment which women are obligated in, as we learn explicitly in Deuteronomy 16:14-15.
Abaye essentially exempts women from an independent commandment to rejoice on the festival. The husband is obligated to make her happy, but she herself is not obligated to rejoice. If she is a widow, then those men who are accompanying her (chaperones?) are obligated to make her happy.
As a side note, we can see here the development of a rule. The rule that women are exempt from positive time-bound commandments was originally descriptive and prescriptive. It, for the most part, was an accurate description of what mitzvoth women are obligated in. But by Abaye’s time it becomes prescriptive, for after all, rules are not really rules if they have exceptions. Abaye uses the rule to exempt women from a mitzvah they were previously obligated in.