Mass e-mails of this type very rarely see high levels of engagement, partly because they don't generally seem particularly important and are easy to ignore - as Dukeling touches on in his comment a meeting is more likely to a) get responses and b) impress a sense of urgency and importance that a general canvassing e-mail will.
Something else I picked up on is:
I often send out emails
I'm not sure exactly what you mean by "often" but if the frequency of these e-mails is too high you may actually be contributing to people's views that they aren't important and reducing their impact. They can easily become nothing more than "background noise".
Let's look at your specific points:
The laziest (i.e not outright lazy) coworkers will not engage in this discussion 99% of the time
If they already have a tendency towards laziness then it's probably not a surprise that they don't willingly engage with optional tasks.
Ultra-busy coworkers will not engage in this discussion 80% of the time
Again this shouldn't be a surprise - if someone is "ultra-busy" with their actual work then they are unlikely to be taking time out of these tasks to look at something optional, even if it was something that they would otherwise have wanted to have input on.
Managers/coworkers not in my core team (i.e people from adjacent teams in the same department) basically never bring anything to these discussions unless it's in their main scope of responsibility
Why would they? Their area of responsibility is, by it's very definition going to be the area that they look at and I wouldn't expect them to be sticking their oar in to other teams.
Honestly I think the problem you have here is either an unrealistic set of expectations, a poorly communicated message or a combination of the two.
Dukeling's suggestion of having a meeting is probably the best way to go at this point, it's more likely to get people involved and will give you a much more accurate gauge of how "bothered" your coworkers are (or not as the case may be).