There a number of arguments as to why this is the case and the article touches on these:

• One could make an argument that most drivers don't use their spare (or don't know how) and would call for roadside service anyway.
• Another argument is that the extra weight of the spare has to be hauled around for months or years before it gets used, if ever, and fuel is used for that extra weight costing the owner and increasing carbon emissions.
• More pragmatically the most likely answer is the auto makers found out they could simply stop giving out spare tires and it doesn't cost them any customers, and increases the auto maker's profits. Some will even sell you a spare tire at an extra fee meaning even more revenue.

My guess is of all these reasons, the third answer, cash grab is the real answer. The author gives us one sentence, but agrees with me.