As a quick answer, the Russo's along with writers Markus and McFeely stated on the feature commentary that one of the main choices for the use of the particular time travel apparatus was simply due to the fact that its inception was already pre - figured in the plot, thanks to Peyton Reeds Ant-Man films which both set up the notion and mechanics of the 'Quantum Realm'.
Following consultations with actual theorists, they settled on the choice due to both the above and also the notion that the method removed grandfather paradoxes and the like, allowing for the mid - point reintroduction of the 2014 Thanos, Nebula and Gamora and all sorts of similar silliness without the audience picking up or pulling on too many exposed plot threads which, like any other time travel movie, naturally make less and less sense the more the viewer looks into them.