A: Yes, Cabrillo is the standard format for most amateur radio contests. But Cabrillo does not meet the needs for contests that require distinction between digital modes. Cabrillo only allows the use of the mode designator "dg" for all digital modes. That doesn't allow us to confirm that the specific digital mode is PSK31, as required for most 070 contests. That also doesn't allow us to distinguish between the multiple PSK variants that are allowed (and encouraged) during the "31 Flavors" contest.
Therefore, we require ADIF submissions, because the ADIF format allows for (and enumerates) all of the PSK variants that we need to see.
ADIF is a standard format, and all logging programs are able to generate it. In fact, that is the standard used for all electronic QSL services, such as eQSL, LoTW, QRZlog, etc. And there are multiple other methods that can be used to generate ADIF if an operator is not using a commercial logging program. (Do an internet search for "text-to-ADIF converter", for example.)