While the other answers are correct, the fundamental "why" is one of few things
Cognitive load users are trimming "superfluous" information because of the amount of possibilities being presented. Many sections (Versions, Benefits, Personal Details, Features, Payments) with fair amount of complexity in each to consider and all at the same level of visibility.
When users do this automatic mental trimming in an unintended way the UI is in trouble.
Use sections to direct this mental modelling.
does user want more than one? If user is clicking to "pay for 5" option but have only ordered one can not assume they actually want multiple. May be a misunderstanding (as below). Only missed the "quality" if sure actually wanted more.
How do you know quantity intended?
does the payment options affect the number purchased or vice versa? Do not assume user understands your business terms as well as you do
- user may only want one but mistakes the payment options that are appropriate for their choice
- or they think that the payment option should automatically override the number intended to order
Where possible remove "gotcha's" rather than educate user