With older technology engines, especially, reversers hanging up when commanded to restow in a dynamic situation were a real hardware concern.
Hence the admonition - reversers out, aircraft stopping.
Can recall this being a contentious issue at the enquiry into the Sydney crash of VH-AAV in 1980. An AN B727, landing at the time, had conflicting ATC instructions (as I recall) and, once the buckets were out, the Captain (BG) declined further instructions to go around.
The reality is that it takes some time to get the reversers stowed and the luxury of contemplative time is one commodity the pilot doesn't have in the situation where he/she is contemplating a go around from the initial touchdown.