By the time “airplane mode” became common on mobile phones, the phones installed in airplane seats were already decommissioned in most cases.
They can't do this because it would destroy their credibility with the ignorant as much as it has with the informed, that would get a critical mass. So yeah we have "flight mode" and every single flight someone breaks it. It isn't remotely enforceable so it is just as well that connecting to cellular is harmless. (Planes also have expensive wifi instead of expensive skyphones now, so the financial incentive remains.)
Airplane mode was a figleaf to counter "your phone must be switched off" which was the old-school airplane mode enforcement.
Undermining security for little bits of money for special interest. The naked corruption of purpose could make you angry if you let it.