Why don't planes have wifi?

More and more planes have wifi. Major airlines in the United States, the Gulf and Europe offer it on most of their long-haul fleet and on a good part of their short-haul fleet, and some have made it free with the arrival of low-earth-orbit satellite constellations like Starlink. What remains true is that connectivity is not universal: many regional flights, low-cost carriers and older aircraft still don't offer it, for technical and economic reasons rather than legal ones.

A plane can't use an ordinary mobile network at 11,000 m of altitude and 850 km/h. It needs an antenna on the fuselage that talks to geostationary or low-earth-orbit satellites, or to special ground towers in air-to-ground systems that only work over land. Installing it requires modifying the structure, obtaining a supplemental type certificate from the FAA or EASA, wiring the cabin and accepting the small increase in drag and weight from the radome. It's work that grounds the aircraft for several days, so airlines schedule it to coincide with major overhauls.

On a one-hour flight, few passengers pay to connect, and satellite bandwidth is billed by volume consumed. For years, the investment didn't pay off for a short-haul carrier; that's why wifi arrived first on long-haul routes, where business passengers value it and the plane spends many hours connected. Falling satellite costs and competitive pressure are changing that calculation, and new aircraft now roll off the factory floor already equipped. The wifi that's still missing today is generally a matter of time and fleet age.