I had an occasional small glass (sherry glass or shot glass) of wine intermittently through my second trimesters because I like the taste. I don't drink to get drunk. I don't drink coffee or tea. I've never smoked or taken drugs. Quite frankly in the first half of pregnancy, I could barely even eat food thanks to the bone wearying nausea.
Having spent 4 months longing to vomit for a temporary relief, then segueing seamlessly into incapacitating SPD that eventually had me near housebound in constant burning pain, forgoing a few sips of something pleasant every few weeks was a step too far in loss of pleasure in the physically deeply unpleasant year (x2) of pregnancy and postnatal healing phases. Then there was the nearly 3 years of breastfeeding...
(oh and the months of not driving because I couldn't fit behind the steering wheel/ was recovering from surgery/ birth injuries)
I'm a light drinker and was happy with my ability to stop after a few mouthfuls. I can go weeks without drinking. I wouldn't do something like Dry January because there's nothing to prove. I can go that length of time without thinking about it anyway.
The advice was slightly more relaxed then and previous generations haven't been full of FAS from mums drinking Guiness recommended for iron in older generations.
The advice has been made blunt and overly simplistic because many people don't understand what a unit is and mistake a large glass for one when it's 2 or 3, and think they're drinking lightly when they're half a bottle through. It's also not ethical to thoroughly research a "safe" threshold.
That doesn't mean that small, occasional amounts are definitely harmful, or that anyone who misses the taste on a few occasions has an alcohol problem.
TBH, I probably put my babies at higher risk by driving between months 6-8 with my bump rubbing the steering wheel and getting the seat as far back as I could reach and see to fit in the car. Month 9, I couldn't fit anyway (and was trapped in the house unless someone else could drive me door to door)