[RexetBlell]

The developers were thinking of doing this at the beginning but decided against it.

Currently, when you send a transaction, the transaction includes a gas price that you are willing to pay for a unit of gas. The miners then decide if they want to mine your transaction, or not. Each opcode in the Ethereum Virtual Machine requires a different amount of gas, which is hard coded (look at this spreadsheet: https://docs.google.com/spreadsheets/d/1m89CVujrQe5LAFJ8-YAU... the opcode that is causing trouble today is EXTCODESIZE which has a gas cost of 20, which is apparently too low).

Initially, there were ideas where you could specify in the transaction the gas price you are willing to pay for each opcode. But this would make transactions very large (in terms of bytes).