How does sending manuscript to new reviewers close the review loop?
To me, a review process has to be closed just like a loop, in that those who comment on a manuscript should assess the resulting revision.

So you submit a first version of the paper. The editors invites some reviewers to submit reviews, and Reviewers A and B accept the invite. When Reviewer A accepts the invite, they have no way of knowing how the process will evolve. They know that they have to submit a review within a fixed amount of time, upon which three outcomes are possible:

accept as is;
reject completely;
recommend to revise and resubmit.

The first two outcomes mean that the process ends there. But consider what happens when the third outcome happens. An amount of time X will pass for the editor to make a decision, and Reviewer A has no way of knowing how much time, particularly since Reviewer B may be late with their review. Then, the editor will give an amount of time Y to the authors to perform their revision. Maybe you, as author, are very eager, and you only use an amount Z&lt;Y of that time. So at some point, you resubmit your revision, and Reviewer A will be invited again to give a review. But X+Z time has passed. When Reviewer A was invited for their initial review, Reviewer A had no way of knowing:

whether any number of revisions would be necessary;
how much time X+Z would be.

Maybe Reviewer A finds themselves overloaded with teaching tasks when the invitation for reviewing the revision lands in their inbox. Maybe they had set a month apart for redecorating their house. This is why reviewers cannot, in general, be asked to commit to reviewing more than one iteration of a paper at a time.

You have run into bad luck to have been confronted with a completely fresh slate of reviewers twice. It is not nice to have to chase after a moving target. The prudent thing to do is to summarize the conflicts in the feedbacks, and send a message to the editor. It is their responsibility to resolve such issues, but they may not be aware that any issue exists. So you should make the editor aware.