Since then there have been advances in the range and types of chemicals that have the right characteristics to be delivered by a missile, plus of course in the types of missiles and devices that can deliver the chemicals to the battlefield
but not really, since chemical weapons have always been a failure on the battlefield, they simply don't work against soldiers - a gas mask and a hazmat suit defeats almost all use in a way in which a normal explosion doesn't. They're also expensive, they degrade way more than normal explosives so you have to keep building new stocks.
The countries banned them, not because they're amoral, but because they don't work, so there's no problem banning them, land mines are just as amoral, but the countries keep those (or stay in defence alliances with countries which keep them)
Obviously as a fear weapon, and against unarmed people they're a bit more effective, but still less effective than conventional explosives, remember the Skripal's survived an individual targeted attack, remote delivery of large volumes is a huge waste, the only person who died in Salisbury sprayed it themselves directly onto their skin in large volumes.