Oppo doesn't have that issue in EU and ships 7500mah just fine though. Some also split batteries into two just to accommodate this.
Split batteries are also better for efficient space usage (depending on the chassis) and longevity.
They split it up into multiple smaller cells to do that. Or don't ship by airmail.
A better phone sent by horse would get to my hands sooner than a phone I don't give a shit about that can be shipped by airpost.
I moved from high end to a "mid-range" Samsung phone that's way better than it needs to be given how boring phones have become. The only upgrade I wish on it was more open source software.