Having to sort trash and manage a biological process are two that I can think of.
Industrial compost sites and anaerobic digesters are likely a bit smelly. People also may gripe about having a compost bin in addition to a recycling and trash bin.
Aerobic compost is not smelly. Anaerobic fermentation caused by not mixing in enough oxygen is very smelly and slow.
Yea, smell issues are from transport of the food waste to the facilities. If you have a facility accepting waste, there will be trunks bringing in smelly stuff on a regular basis.
Cynical hottake, 150B of food waste per year in US, aka one mans trash is another's revenue.