Grease trap deterioration does not happen overnight. It starts when microorganisms in your kitchen waste breed inside of the grease trap and digest the grease and food waste. This process causes the contents to turn acidic (lowering the pH). The longer you wait between cleanings, the more acidic the waste becomes. This acid environment erodes the concrete and metal that comprise the grease trap.
At first, the surface of the concrete erodes until you can visibly see the rebar that supports the concrete. When this happens, you can see a grid through the concrete surface. Eventually, the concrete erodes to the point that rebar is exposed. The structural integrity of the walls and floor of the grease trap are compromised as the acid dissolves the metal rebar.
Eventually, a wall can collapse, which both makes the trap less effective and can lead to a collapse of the trap itself. You might find that a sinkhole suddenly develops in your parking lot or drive-thru where your trap is located, risking the safety of your customers and employees.