* "other email providers shortly followed suit" means that it was never out of their reach to begin with, they just needed more competition to convince them to try: which didn't have to be Google and didn't have to be ad- or surveillance-supported.
* 1GB storage in 2004 to 15GB storage 21 years later suggests that something vital has stalled. Every other storage metric (price of RAM per MB, price of hard drives per MB, price of cloud storage per MB) has improved 100 fold over the same time period[1,2].
Which freemail service isn't ad- or surveillance-supported?
> suggests that something vital has stalled
Why does it have to be a technology-driven limit? I dare say Google thinks that anyone with more than 15GB of email is a serious enough user to pay for it.
> 1GB storage in 2004 to 15GB storage 21 years later
The original marketing was the the storage would grow forever, and you could believe it. Google was riding the an incredible high from smashing out what felt like constant Amazing New Things throughout the noughties. In fact, when they originally made the claim, back when Don't Be Evil was still the motto and they hadn't bought DoubleClick, I'm sure they believed it. By the time the final upgrade (or rather joining, of 5GB photos/Drive to 10GB mail) to 15GB came round in 2013, there was definitely a hint of the horns in the hairline.
It could also mean that you can't invest indefinite amount of storage to ever growing user base, if storage metrics would not improve indefinitely. There is a break down and 15GB cap is nothing comparing with Google Photos cut, which is a strong sign that storage is the problem even for behemoths.
* 1GB storage in 2004 to 15GB storage 21 years later suggests that something vital has stalled. Every other storage metric (price of RAM per MB, price of hard drives per MB, price of cloud storage per MB) has improved 100 fold over the same time period[1,2].
1: https://ourworldindata.org/grapher/historical-cost-of-comput... 2: https://jcmit.net/memoryprice.htm