Where'd you hear that lie? Stats are very important in BECMI: high STR meant damage bonuses, high DEX meant ranged attack bonuses, high CON meant Hit Point bonuses, high INT meant bonus languages, high WIS meant bonuses vs. Magic and high CHA meant bonuses to monster reactions rolls. PLUS, each class had a Prime Requisite that, if high enough, provided an X.P. bonus.
The "stats don't matter" nonsense comes from a tiny clique in the ttrpg community who believe rules shouldn't dictate how they RP their character. If a PC has a 6 INT, they're literally a moron, but some people think they can play that PC as a super-genius if they want. Why? Because this tiny clique of "gamers" have no idea what roleplaying is.
But use your common sense: if an ability score has any impact on the fiction or mechanical function of a game, that by definition means they matter.