This is an uneducated, and wrong opinion. No really active project ever will reach 0 number of issues, unless nobody is using it nor testing it. Most really active projects do indeed all have tens if not hundreds of open issues (and PRs). That's not the reason.
1) There are still a bunch of pending issues.
See above.
2) They are still tweaking some feature (BIP 70 in, BIP 70 out as an example) once you have a 1.x version taking out a feature in financial software can and has to take multiple years.
Taking out things
is already taking years (not that it should in some cases). BIP 70 should have been removed ages ago, among other things. It gets discussed, agreed upon and then they wait. Then in some major revision they disable it on default (see, not yet removed). They remove it completely only in some subsequent major version. Years.
You need to look through Github discussions or read the IRC chats. Bitcoin software is by no means anywhere close to 1.0, if it ever gets there that is. This is just a flaw in most humans, you're trying to assign meaning to something meaningless like a 1.0 version number. If instead of 0.19.0.1, the last released version was released as 1.0. What difference would there be? None whatsoever (other than an play on emotions - look at the part about the flaw again above).