Just gone through the experience of deleting Instagram. Get this:
1) you have to "request" a deletion of account (not "decide");
2) you cannot do this "request" from within the app itself;
3) you have to have your password;
4) if you have forgotten your password, you have to log into Instagram to request a new link to be sent, and
5) you cannot do 4) without allowing Cookies.
6) even if they 'grant your request', there is a month-long delay before the account deletion.
Something tells me they don't want deletions.