I would much rather an adventure path be way more sandbox...
Yeah, but it is called an adventure "path" for a reason. They tend to sell well because it doesn't require the GM or players to do a lot of work choosing what thee adventuresome bits will be, and links them together in a rough string that should result in a satisfying story when all is said and done. Simply put - adventure paths are for people who don't want (or don't have time for) the extra work required of playing in a sandbox.
Yes, they are railroady. No argument. But that's part of their appeal to the market, so I wouldn't expect that to change.
Moreover, from a developer's point of view, sandboxes are inefficient. In a path, you can expect the players to hit almost all of your content. In a sandbox, the PCs are expected to wander around, and ignore or skip large amounts of content. So, the developer has to present much more content than the player's are going to use - that means, a path that takes you from level 1-15 takes less development effort than a sandbox that does the same thing. Sandboxes are thus more expensive than paths to produce, but I don't think the consumer thinks in that manner, and may not be wiling to pay the extra cost.