Which trains have Wi-Fi?

Acela.
Adirondack (not available in Canada)
Amtrak Cascades (not available in Canada)
Amtrak Hartford Line.
Auto Train.
Blue Water.
Capitol Corridor.
Cardinal.

Is there free Wi-Fi on trains UK?

Most British train services now provide free wifi as standard but the DfT has told its contracted operators in England that they should cease offering it if they cannot justify it financially.

Why does internet not work in train?

As the train zips along, its routers must keep up by hopping from tower to tower. A gap between sites can interrupt service. On stretches with underdeveloped infrastructure, such as rural areas, passengers will find themselves time-traveling to a pre-internet era.