I'm not sure if I understand how this is necessarily a bad thing. Perhaps I'm wrong about what blast zones are. Please correct if this is explanation is erroneous in any way:
The blast zone is the area in which a KO occurs. It surrounds each stage on all four sides. Once your character crosses the invisible line into said territory called a blast line, they will instantly die. To extend the blast zone means to push the blast line that divides the safe and death zones of a stage even further out from the center.
Now if that is indeed correct, it would mean that while characters could be sent flying further from the stage without crossing the blast line, it would also increase the distance they needed to cover in order to make it safely back onto the stage as a side effect. This would create three basic scenarios:
1. Percent is so high certain attacks if landed will instantly kill them
2. Percent is high enough that when launched off the stage with strong KB certain character's recoveries won't allow them to make it back to the stage due to the increased distance needed to travel.
3. Percents is at a point where when launched, a character can easily make it safely back onto the stage unless they are edge guarded.
Now obviously in what direction they're launched will be important. If you try to hit them straight up hoping for a star KO let's say, the blast line being further back will indeed be in their favor as if they aren't launched past it, they'll likely be above the stage already and only need to land on it.
Certain characters have recoveries that are strong in one direction, but poor in the other. That is to say, horizontal vs. vertical distance covered. Still others have recoveries that are strong in both aspects, but leave you open to attack. The key will be knowing in which direction to launch each character to make it hardest from them to make it back on stage and then edge guarding to ensure they don't succeed.
I'm not sure what the point of this post was. It was correct, but I don't see your point.
If you're wondering why this is bad, it's because:
1. It limits character viability because some characters simply lack the tools to deal operate in larger blast zones.
2. It means you aren't rewarded for your "hard reads". As an example: In a tournament I watched today I watched someone forward smash another person out of a roll. The commentators were stunned and shouted "OH THAT WAS AN AMA- oh never mind he's living." It kills momentum and hype greatly to see your hard work not pay off. Why would you play a game that becomes a tedious task to do basic things which are essential for a win condition? The audience isn't exactly friendly toward that either.
3. As somewhat covered above, the audience gets bored. It isn't interesting to watch someone smack around his opponent who is at 140%+ because he can't kill. The main response to this is "oh, well just jump off stage and hit them". My response is that even then you generally won't finish your opponent off, and not only that, why should someone who is winning have to take such a massive risk just to complete his lead? You are putting your entire gamelife on the line by jumping offstage JUST to seal what you've worked so hard for.
TL;DR: This game is anti-hype and anti-competitive because players are not rewarded and viewers have to sit through anti-climatic mundanity.
EDIT: On a final note, I'd like to point out that I have no issues with the massive roll buff. In fact I believe it promotes very high level play through reads and intelligence. But the blast zones also ruin that as shown in the example I used in Point #2.
