Well, everyone except the SF and Swads use 7.62, BOF has lines producing upwards of hundreds of millions of rounds every year, I reckon they aren't switching to nato 5.56 due to convenience and for the fact that we have tons of 7.62 stockpiled probably..
Besides 5.56 has lower penetration over distances and packs a weaker punch.. Any conflict inside or outside Bangladesh will be urban and in close quarters.. in a situation like that, I'd take 7.62 over 5.56 unless you want some dude with level IIIa body armour to not stay dead.
And remember for 5.56 we'd have to set up new production lines not only for ammunition but for the guns themselves and that screams logistics issues..
But If it we're upto me, I'd start producing 5.56 in limited numbers for SF and SWADS, then get TOT for guns, then in good time switch to 5.56, just ease into it instead of buying millions of guns and then having a slow transition that will take a decade, If not longer.
And yes, 7.62 is not nearly as accurate as 5.56, 5.56 is a fast round btw compared to a 7.62.. it has some pros too.