Reverse thrust on high-bypass ratio underslung jet engines (ie most modern airliners) is not a good idea due to the high risk of FOD ingestion and engine damage.
Reversers are usually required to be at idle thrust by about 60-80kts forward speed - ay high thrust levels the amount of air scooped up by the intake is huge, and if stationary on stand would probably pick up all the baggage labels, gravel and loose nuts and bolts within a sizeable radius.
Not such a problem for aircraft with fuselage-mounted jet engines or props, as described above.