My experience after having some of the same frustrations in Thailand is that the tropics just have such ideal habitat everywhere, it's too difficult to narrow down exactly where a creature will be. In a dry climate you can search for the moist spots, in a cool climate you can search for the warm spots. But when everything is is warm and moist, a snake could be anywhere, and it's quite difficult to narrow down where they actually are. On top of that, the "anywhere" can include deep within water vegetation, in the treetops, or other spots that might be unlikely under different conditions.
I wasn't able to herp Bangkok constantly, but in getting out once or twice a week I often would have been overjoyed with 10-snake months. I had several 1 or 2 snake months during the drier season, though in prime conditions I also had two 7-snake days (counting blind snakes, of course - not counting brahminy blinds I could brag about 4-snake days at most).
I'm telling you, after 11 years in Singapore (for those who don't know, is a small island of the coast of Malaysia), a few hours flight from Kuching, I have yet to flip something with a herp under it. No kidding, I haven't found any proper animals under cover, let alone one brahimny blind snake (which is pretty pointless, I could go to Hawaii for that), ants and spiders.
While Bangkok was tough, it definitely wasn't at the extreme that Kuching and Singapore appear to be in that respect. I rarely got out of the city and didn't have transportation, but just looking in local parks and empty lots, this is what I found under cover via flipping:
3 White-headed Blind Snakes - under logs and a rock
20+ Brahminy Blind Snakes - under everything
3 Red-tailed Pipe Snakes - under AC and a log
1 Sunbeam Snake - under AC
1 yellow-spotted keelback - under AC
1 Copperhead Racer - under concrete
3 Banded Kukri Snakes - under logs
1 Striped Kukri Snake - under log
TMTC geckos (spinytail house geckos, Sri Lankan house geckos, and stump-toed geckos)
TMTC skinks (bowring's supple skinks, short-limbed supple skinks, and common sun skinks)
TMTC microhylids (Asian painted frogs, ornate narrowmouth frogs, and inornate froglets)
TMTC Asian grass frogs
TMTC common Indian toads
Outside Bangkok I've flipped those same frogs and lizards, as well as:
3 Yellow-bellied Water Snakes - under rocks in or near water
2 Collared Reed Snakes - under logs
7-8 Siamese leaf-toed geckos
1 Cardamon slender-toed gecko
5-6 speckled forest skinks
1 long-tailed sun skink
TMTC sapgreen stream frogs
So is Bangkok just far enough north that it's not subject to the "super-tropic" effect that makes it so hard to find stuff under cover in Singapore, Malaysia, and Indonesia?