probably those banks offering only 2.6%pa are flushed with cash, or have alternative sources where they can get funds. thus not keen to attract more depositors.

in theory customers will just go to those banks offering 2.75% but in reality, there are a lot of other factors preventing them doing so - inertia, locked-in by other products, inefficient knowledge, blind loyalty etc. so these 2.6% banks will still get their share of depositors.

for me, very simple, i'll just switch to other banks and will encourage everyone to do so. anyway pbb has almost consistently offer the lowest rates for depositors, so no surprise there. their only "premium" all these years has been their "solid" image.