Gankers could choose to use 250M isk ships to gank with. Miners can choose to use ships that cost 12M isk to mine with. They just don’t make these choices.
Gankers choose 12M isk catalysts because they’ve done the analysis to determine the tool that will get them the most results for the isk they spend, while a miner who is dying to gankers in a 250M isk ship has obviously not put enough thought into which mining ship and fit will yield the optimal amount of reward for their isk investment.
These inequalities exist because there exists player choice and the possibility of making bad decisions that have significant costs, or good decisions that minimize those costs.