Ask yourself this: have you ever downgraded to a C or E class module from an A-grade for the purpose of reducing your rebuy? And I'm not talking about a temporary downgrade because your reserves are out and you don't have enough for rebuy, but instead a deliberate long-term choice to reduce rebuys over successive losses.
*Waves*
I do this!
Sort of...
I don't install expensive armour in my non AX ships. Mainly because it's expensive, and pushes up my rebuy needlessly, but also because I rarely die, and when I do, the armour would have likely not saved me.. *cough*station guns*cough*...
So it's a pointless expense to be lugging around, when in some cases I could own an entire other ship. Lol
That and jump range, speed and manoeuvrability are more fun than not dying.
But then I don't hoard credits unless I'm saving for something specific, because I like being low on credits so my big ships aren't expendable.