Why do conferences keep deferring the deadlines? We work on some research problem, obtain some publishable results, then we target an international conference to disseminate the results and methods in, and then there is a 'last' date or deadline.

We submit the complete manuscript to the conference on or before the mentioned deadline of the conference.

Then, suddenly we see the deadlines (both for submission and for the acceptance) continually change over time. For example, in one of the last year's Computer Science conference, the deadlines were changed repeatedly. Please note that the deadlines for submission were getting extended on the very day of the earlier notified deadline, which is another demotivating factor.



Why might it be happening?


Because the targetted number of submissions were not received.
The reviewers could not meet the deadlines.
Can there be any other reasons than the above two?


I have the following questions:


If the conference organizers were not so firm about this stuff, why did they even have an important date page?
It is actually frustrating for the authors who have submitted the paper on the first submission dead line and still waiting for 3 months to get the review. This is ridiculously bad for a conference.
The papers which are submitted at the last notified deadline will be reviewed in a less productive way. If this is true, then what is the point of having a peer review?
In such a scenario, is it advisable to withdraw the paper from the conference?
Does it not hamper the quality of the conference as good researchers would not submit to the same conference again in following years?


I believe that this question is not a duplicate of this question.
There are basically two approaches for conference deadlines.  In my experience, top conferences have a "hard" deadline and do not slip it, and the rest frequently slip it once.  Usually the slippage is actually planned, and it's announced pretty far in advance: for instance, a conference might say 2 weeks before its announced deadline that there are actually 3 weeks to go.  Sometimes it's a panic because of low submissions, which is probably a bad sign.

Notifications are another story.  It's considered poor form to miss the announced deadline, though if the change takes place before submission (delaying both submissions and results) that seems ok: people can choose not to submit.  Simply missing and redefining the deadline isn't playing by the rules.

I wouldn't say that the changes to the deadlines are a reason to avoid a conference.  Many factors go into the decision about which conference you submit to.