Good security and decentralisation: Due to Bitcoin's PoW consensus model, it is extremely expensive for an attacker to attempt to censor or rewrite transactions. Bitcoin also has a large number of nodes (>10000), providing more decentralisation than Stellar.
Big partner ecosystem: Bitcoin has a large number of partner companies looking to improve different aspects of using and getting on to Bitcoin.
Improved functionality: Bitcoin has more opcodes than Stellar, and the platform can implement more complex functionality.
Good Liquidity: Bitcoin is the most traded cryptocurrency asset. Hence liquidity on popular markets is not of concern.
On chain verification: Bitcoin Script is verified on chain and the platform need not be trusted for performing correct computation.