Well, I can't speak for Microsoft, but I imagine it's because it's a
very rare case, and allowing for a single form to subscribe to an
event multiple times would result in 99 mistakes for every intended
usage of the feature.

I've built a lot of Windows forms. I often have multiple event
handlers for an event, but I've never had multiple handlers within a
form subscribing to the same control event.

In fact, if I understand your scenario, I would be more inclined to
code it as each event handler calling an internal routine to do the
real work, so if there are four controls raising events, and three of
them do the same thing while clicking the fourth control (or whatever)
does the same as the other three plus a bit more, I would code it like
this:

private void Control1_2_3_Click(object sender, System.EventArgs e)
{
   DoSomething();
}

private void Control4_Click(object sender, System.EventArgs e)
{
   ... some additional code here ...
   DoSomething();
}

which allows me to set the event handlers in the Designer GUI, _and_
gives me full control over the order in which things happen within the
fourth event handler.

Small point off the topic of events, but to save confusion - there are
several Java IDEs. Netbeans is only one of them.