I would never rely on an airplane's wifi to enable reliable streaming (if it's even permitted in the first place).

There are a plethora of places to download content to your device for offline viewing, be it Android, iOS, MacOS or Windows.

Of course you can also hold the equivalent of 10 Libraries of Congress on the devices today for reading too so I fail to see any reason someone who is keen on having something to help pass the time wouldn't pre-load their device with the content they know they'll enjoy.

As said, IFE breaks. Planes get swapped so you may book a flight with advertised IFE and then find it's not there after an equipment change. Sometimes the content they provide isn't so great (or you've seen most of it).