Why don't miners charge more for high value transactions? I know high and low value transactions take up the same amount of space in the blockchain. 
But wouldn't btc be more economical and fair if miners deliberatly chose transactions based on the value/fee ratio?
That way small transactions became cheaper and more viable
Miners don't charge anyone.

Users put aside some amount of satoshis to incentivize a miner to include a transaction in a block, as the miner takes those satoshis if they are successful in mining that block.

A miner has the incentive to maximize their own profitability by including the highest paying transactions into their block, and to squeeze as many in as possible to maximize that revenue.

The idea that miners might reject some large value transactions because they don't pay a higher fee is incompatible with their incentives, which are to compete with other miners for those transactions which pay the most per weight unit. If a miner decided not to include transactions with sufficient fee, some other miner would include them, and be more profitable than the miner who didn't. It only makes sense then that the miners will continue to operate as they currently do because attempting to adopt a strategy like you suggest would be harmful to them.

Ultimately, miners do not control anything. They merely attempt to profit from what the market is offering.