Another 'sitting down' dog here

Pebbles nearly 5 months has always done this. Sometimes worse than others. TBH sometimes she's not even keen to go on a walk which seems really strange. Once she's out she tends to sit down or lie down even when she sees children/people or other dogs in the distance and just wants to watch them for ages hoping they will come to talk to her.
Anyone also experience the problem with constant sniffing of everything on the walk which means very slow progress?
