Yes players tour around almost nightly but the teams cannot formally offer them a deal - Most players tour many arenas so your not convincing me they commit ( even verbally) until they have looked at all options. What changes is the US programs can shove a piece of paper under the parents noses and yes the US programs are a good option for most so the parents who have not see anything formal from any team because they have no idea who is going to draft them so parents are parents and the old bird in the hand thing. You may say that parents and players have an idea where they might go in the OHL but that is only for the first round or maybe part of the second round - leaves a lot of kids and their parents thinking this may be the best offer I ever see so lets sign now.
The timing of the draft doesn't really affect much in terms of kids going to school. It may affect some in terms of where they will report versus other options but moving it back combined with allowing current players to be dealt may help balance things out when teams have the option to move up while others have the chance to pick up other assets when BPA at their selection won't report.
Again, it provides more balance and opportunities for teams that may struggle on draft day ultimately leading to increased competition across the league.
An example
Going into the 2018 draft, using DiPietro and Ottawa as an example only.
Let's say DiPietro would report to Ottawa but in the first round BPA would not, DiPietro to Ottawa for their first round pick would make sense, would get a player to report who otherwise may not and Ottawa gets a player they covet.
If a kid won't report regardless then when the draft is held doesn't matter.
If they will only report to certain teams, again when doesn't matter but having the picks to acquire their rights if they are defected would matter and if those picks aren't available the kid may never report or a team may not get full value.
Being able to expand trading options on draft day by moving it back ensures teams get value by dealing their pick instead of walking away from a kid for nothing because they won't report, especially in the higher rounds.