Bank notes or numbers on my banking account secure the capital that I invested in them because the borrowers are forced, via collateral, to use these notes or numbers to repay their loans.
In a similar way, blockchain secure all the bitcoin transactions. The bank notes can be printed by the government making its value less with more increase in supply but in case of bitcoin, its value will keep on increasing. Think if you hold 1000$ in dollar and 1000$ in bitcoin (which you call numbers) from 2010, you would have become millionaire by now. This is the potential of bitcoin which you are repeatedly ignoring.