That only works in certain countries, where sim cards & data are...

That only works in certain countries, where sim cards & data are cheap & easy to buy. Some countries that are relatively cheap (eg. Spain), or very cheap (eg. Bulgaria, Poland, Vietnam) don't have those cheap options at the airport. Other countries that you think would be cheap charge moonbeams (eg. Italy, Hungary) and/or make it extremely difficult to buy (eg. Hungary). And believe me, it's annoying to have to find a store (that can be difficult to get to and then wait in line) to go & get a sim card. Been there done that & if I had the option to roam cheaply with access to important travel & communications apps I would much prefer that.