I think because that’s what customers want. Very few customers send that many SMS messages, especially nowadays that Internet-based messengers have mostly replaced them; but a lot of customers want a large Internet data limit in order to watch short videos or things like that…

FWIW, looking at providers in my country, I found:

• 1500 minutes or SMS: www.yesss.at/en/tarife
• 1500 or 3000 minutes or SMS: www.s-budget-mobile.at/home
• unlimited minutes or SMS: www.redbullmobile.at/tarife#Sim-Only-Tarife www.magenta.at/handytarife/tarife-ohne-handy#0 www.a1.net/handys-tarife/tarife-ohne-bindung www.drei.at/n/telefonie/tarife/sim-only-tarife

So your premise is not exactly true, at least not worldwide.