Because humans tend to think in the short term and for-profit entities are happy to oblige. It could be argued there are many things which we are morally oblig

Because humans tend to think in the short term and for-profit entities are happy to oblige. It could be argued there are many things which we are morally obliged to stop using plastic for, as it only serves as a convenience. Disposable food trays and "silverware", straws, individually wrapped things, and so on. Society could adjust to bringing their own water bottles to be filled at restaurants/gas stations/work, but between laziness on the consumer and the profit motive of selling cheap plastic bottles for $3 by companies, we don't. Then there are plenty of things for which plastic is useful, durable; and instances where even single-use plastic can be justified. But on the whole, society is trading the environment tomorrow for convenience and money today.