I think those are remnants of the old system when you could only pick one tile objects and those items could be picked one tile at a time. However, across the updates you can now pick multi-tile signs and things such as Map of USA as whole, so I think this mechanic should apply to the following items as well:
Fancy Brown Rug (6 tiles)
Dark Purple Rug (6 tiles)
Child's Drawing in Muldraugh Elementary School (5 tiles)
Children Drawing in Muldraugh Elementary School (3