I never understood the logic behind this but then think the 180 day was launched only recently as Black Friday 2018 it was only a special. I guess they just never updated the bundles. Their site is a mess though. It's zero rated but Recapcha is not so you can't buy anything without airtime and it also redirects to your banking's site. This is a major oversight.
I would also like the option to use my airtime balance as I need to take the sim out of the modem to use ussd.