There are plenty of cheaper, better MVNOs than Mobile X.
$4.08 a month for 1GB on Mobile-X
is a better value than
$10.00 a month for 1GB on Good2Go
I don't think there's some other seedy reason - Mobile-X is just the least expensive option I know of right now in the US that can be purchased at retail, so that is probably the main reason
Do you have links to services that cost less, per line/sim? I don't think they exist, especially at retail.