The rising centralization of mining is one of bitcoin's major issues. The reason for this is that the bitcoin mining algorithm runs much faster on mining chips known as asics, which are 10 times more expensive than a standard graphics card, effectively shifting mining to profit-making companies. This will be a major issue in the future because the biggest advantage of all crypto currencies is distributed. Monero's mining method overcomes this, ensuring that the currency will always be distributed.
Another issue with bitcoin is the block size restriction (check bitcoin cash), whereas monero's block size limit is meant to adjust to network size.