Aside from how confusing it is to conflate ship insurance and the corvettes you can get anywhere, any time…
This would break so much of the economy. Corvettes cannot be reprocessed, nor can their starting equipment - this means they do not add any resources to the game when CCP endlessly spawns them for players. Your idea would produce massive amounts of resources for a flat ISK fee that doesn’t change over time. CCP would now be allowing players to buy fitted ships from NPCs for ISK, instead of driving the buyers to draw resources (in the form of ships and modules) from the massive player production system that is the foundation of the entire economy. The mind boggles at the knock-on effects of this.