Because they can print as much money as they want, devaluing yours in the process. Just like they did for the bank bailouts. A trillion dollar wealth transfer from the 99% to the 1%. Bitcoin was designed to solve this, the first block even contains a reference to it. BTC is neutral, international currency that knows no borders and which has a fixed supply and clear, unambiguous monetary policy. Nobody can ever turn on the money printer. It has been faithfully relaying transactions for people for 15 years without a single hack or day of downtime.

It makes functional currency available to anybody with a phone and an internet connection, which matters a lot in the global south and to the "unbanked" and "underbanked". There are billions of people who have cell phones but no stable banking or monetary system or who regularly experience hyperinflation, Bitcoin solves this problem for them. Transactions settle in seconds to minutes which is much much faster than most in-country bank transfers let alone international. Fees can be as low as a penny with Bitcoin's lightning network which can scale basically infinitely.

It does all of this with about .1% of global energy usage, most of which comes from renewables since Bitcoin miners inherently seek out the cheapest electricity available which tends to come from over-provisioned renewables during times of low electric demand. This is massively less electrical usage than even remittance services alone (western union etc) use, let alone the entire banking system and the carbon impact of moving around physical money from place to place.