From the point of view of the employer, there are only two points at which they have useful information to give you:
if they decide to offer you the job
if they have successfully hired another candidate (or decided not to fill the position at all).
Up until one of those things happen, your status is still "under consideration". Even if they really didn't think you were a good fit, they'd keep you "under consideration" until #2 happens, because in theory they might still decide you were better than any alternative.
It can take quite a while until #1 or #2 is attained. They might interview several more candidates, choose someone else, get approval from their dean to make an offer, wait for the candidate to consider the offer, be turned down, make an offer to someone else, etc. This can easily take far more than two weeks.
So while I agree that it would have been nice for them to answer your email, their reply almost surely would not have told you anything useful. Had they reached #1, they'd have told you, obviously. It's very unlikely they'd have reached #2 within two weeks, but if they had, they should have told you that too (though admittedly this might sometimes fall through the cracks). So if they replied, it would only have said "our search is continuing and you are still in consideration, we will let you know when something happens".
Thus there is not really much point in you contacting them for updates, unless you have new information to give them. For instance, "I have received another offer with a deadline of X, so if you want to be able to hire me, you'd better get your act together and send me your offer before then." (Only don't phrase it quite like that.)
On the other hand:
I am in an extremely specialised and competitive sub-field, so I cannot keep on sending out applications, because most of them come back positive with a pre-emptive interview call.
I disagree. You can and should keep sending out applications. If they invite you to interview, that's a good thing.
Later on, I might have to send decline mails for any or all positions that are offered.
That is fine and normal.
And, I know that even as a Group leader it doesn't feel nice to get snubbed.
Declining a job offer isn't a "snub", and no reasonable group leader will take it that way. It's just business. It's not like by interviewing you, they are doing you some special favor that puts you in their debt. They know that good candidates are in demand and will have multiple offers, and interviewing a candidate comes with an inherent risk that the candidate will like some other offer better. It is on them to make an attractive offer if they want to get you.