As someone who works the parade route frequently, I think I can offer a little insight into this issue. First of all, let me just say that I agree there should be more crossing locations for all the parades. When I started three years ago, I believe they still had parade crossings at Casey's and up in front of the castle. I'm not sure, because that wasn't my role back then.
The issue isn't really one of staffing (although more people would be very helpful in general), but one of guests not wanting to do what they're told. We are theoretically always staffed for crossings. The problem is, once we open up crossings, the sidewalks start to jam up as the CMs are more focused on making sure people are actually crossing. For example, some people think the crossing area is a spot you can sit and watch the parade and will literally stop in the middle of the crosswalk. Especially ones that show up right when the parade starts and haven't been able to get an actual spot. So the issue really is between letting people cross, or maintaining the sidewalks. Ultimately, keeping the sidewalks clear in case of a medical emergency is more important. Plus, usually during the day, there aren't really enough people that want to cross to warrant having parade crossings. At WDW at least, management takes safety VERY seriously. Being out in the parade route, even for crossings is a safety hazard. Yes, that goes for cast as well. As someone else said, the floats can't stop on a dime, and the float drivers have very limited view. We aren't even allowed to walk beside the floats anymore.
Also, I think the key difference between WDW and DL is the primary demographic of each park. DL attracts a lot more locals than tourists, or at least the vast majority of them are from the West Coast. On the other hand, WDW draws in a lot more "tourists." The ones that can't (won't) speak English or think they're entitled to do what they want because they paid thousands of dollars to go to WDW on vacation. Trust me, it just creates a lot of issues when crossings happen. Enough that it becomes an issue.
However, regardless of what you think, it is NOT ok to cross the parade route at any time other than at the designated crosswalks. The CMs working the parade route are there for your safety and your safety is more important than your impatience. If that means waiting five minutes until the parade is over, or walking five minutes to get to the crosswalk, then so be it. Patience is a virtue, especially when it comes to your safety at WDW. I'm not trying to sound to harsh or rant here, but no one has any reason to be out in the street during the parade. People in the street is a huge concern, especially for me.