I suspect they may have gone in this direction due to the general unreliability of boat fuel gauges. I can get a 25% change in fuel level depending on whether I am on plane or not. I actually like that Garmin is only decrementing fuel state via consumption and I've found the Garmin calculation to be pretty accurate. I do wish they had more user input available such as being able include a generator fuel consumption factor.To @alnav Al's point, Garmin does not use the trip PGN 127496/7 for fuel info, only PGN 127489 for fuel flow and 127505 for fuel level, only for display. Not quite sure what Garmin is/was thinking not supporting fuel management but they don't really do that even though they have a screen just for that. They could have at least looked at 127505 for fuel level and remaining calculations. This is one of the only bad things I can say about the newer MFD's.
Here is a reference for the PGN's
https://continuouswave.com/whaler/reference/PGN.html
https://www.nmea.org/Assets/20151026 nmea 2000 pgn_website_description_list.pdf
127496 Vessel Trip Fuel Consumption
127497 Engine Trip Fuel Consumption
127505 Fluid Level (pg 122 of Garmin manual)
Garmin PGN list Pg 183
https://www8.garmin.com/manuals/webhelp/gpsmap8400-8600/EN-US/GPSMAP_84xx-86xx-87xx_OM_EN-US.pdf