Because they’re not rising that fast. You have what is likely a combination of land subsidence and ice melt (which may be actually coming to an end) and water expansion from warming waters.*
*Here I’m not getting into Global Warming. Apparently, man contributes about 0.28% of heat trapping gases to the atmosphere, so I suspect most of the sea level rise is due to a natural warming cycle. In fact, as I understand it, NOAA thermometers that haven’t been compromised by the “heat island” affect have shown little atmospheric warming over the past couple of decades. We should consider ourselves lucky — we’re probably heading toward the end of an interglacial period, and then we WILL see climate havoc — of the cold variety.
rocks and pillars on the shore lines around the world and inland show water levels were up 100s of feet from where they are today. that amount of water is now gone. no one will ever convince me that its sitting at the poles in the form of ice and snow...