It isn't just a matter of altitude. The geostationary satellite is a simple bent pipe hanging in space. It returns signals to a fixed ground station that it remains in contact with 24/7. The low-orbit satellite isn't hanging off in space. It is moving, constantly connecting and disconnecting with multiple ground stations every couple minutes. The route between customer and internet is therefore unstable, akin to a cellphone on a speeding car having to negotiation with multiple cell towers. But in this case the cell towers are also each moving on different highways too.

Sometimes there is no up-and-down connection. Sometimes the satellite over the customer cannot 'see' a downlink station. Then it has to bounce your connection along a chain of multiple satellites. Theoretically this should all work, but you don't need to be a physicist to understand the complexity of chaining together so many wireless connections. Ping times will suffer.

AND... there are a bunch of issues regarding the relative speeds of these satellites. They move fast enough that Doppler shifts between them become significant. Satellites have to modulate signals depending on where they are going. That means processing times, buffering ... latency.