Why was the rice component added to 气 to form 氣? 气 is an ancient character that has roots in an oracle bone pictogram, but according to this, the rice radical was added in the Tang dynasty to form 氣.

What were the reasons for this? What does 气, meaning gas, air or life force, have to do with rice?

Note: this question is not about traditional vs simplified.
說文解字 has both references for 氣 and 气.

Put simply, 气 and 氣 comes from different origin and somehow merge together into one stream later.

In detail: 米 is not added to 气 to get 氣 in Tang Dynasty. Long time ago, 氣 appears in the form of Bronze inscription, though different meaning as 气. 氣 is originally designed to mean the "air generated from digesting food". While 气 is originally designed to mean the physical gas. In the reference of 氣, "饋客芻米也" means "氣 is a verb, showing the action of giving guest fodder (芻, chu2) and rice (米) as gift." 饋 (kui4) is "to give someone gift". 氣 with this meaning later becomes 餼 to clarify the action relating to food.

So nowadays, in Taiwan, 氣為餼之異體 (氣 is another non-standard variant of 餼). Also, according the 教育部異體字字典 气為氣之異體 (气 is another non-standard variant of 氣). In China mainland, 氣 is replaced by 气 as standard.