In general, Access has been the "red-headed stepchild" of Office. When Word and Excel were updated to have 64-bit address versions (specifically, that used 64-bit addresses internally), Access apparently was not, probably because every previous database would have tables built using 32-bit address pointers. I suspect (emphasize SUSPECT) that the number of address references within Access that would need to be updated became either (a) daunting or (b) potentially too expensive a task. Specifically, interconversion would become a problem, since a 32-bit database could probably be up-converted to 64-bit with a process not unlike a Compact & Repair - but going back down from 64 to 32 would be impossible once you started actually using the larger address space. Heck, right now if you have a native Access DB converted from Ac2003 to 2016, all you need is a couple of advanced controls or features (e.g. multi-value fields) and you can't Save As (go back to) the old format. With a spreadsheet created for 64-bit Excel but that didn't really NEED to be handled in 64-bit (i.e. small sheet), a conversion process would be relatively easy. All cross-row or cross-column references are by NAME, not by address.
We know from various reports in this and other forums, and from Microsoft's own advertising, that 64-bit Excel can handle million-row spreadsheets. Supposedly, Word has gained the ability to work on very large documents. I have heard less about PowerPoint and Outlook, though I would guess that a 64-bit PowerPoint would handle more slides. I've got NO IDEA what larger addresses would mean for Outlook.
There is a disadvantage here that, for many product libraries that work just fine with 32-bit Access, some of those libraries have not been converted and probably will not work very well with 64-bit environments without some extra work. Many libraries for non-Office products, for example, were originally designed for 32-bit environments, and it is the call sequences that have to be managed to accommodate larger addresses.
I will offer an OPINION (clearly stated as such) that converting JET to 64-bit might be possible, but it would then be a cheaper form of competition with SQL Server. MS doesn't want to compete with itself.