Getting a blotchy finish on softwood despite careful sanding

I sanded a pine shelf through 120, 180 and 220 grit, wiped the dust off, and put on a medium-brown stain. The result looks like a map of islands: dark patches beside areas that hardly took any color. I tested a scrap after the fact and got the same mess. Would a pre-stain conditioner have prevented most of it, or is a tinted film finish the better way to make inexpensive softwood look even? I'm happy to redo the piece if that's what it takes.