There was a time when drink refills were not free, you had to pay for another drink. The arugment was, they gave you straws so you would drink more and buy larger or more drinks.
At some point restaurants realized they could offer free refills as a competitive advantage, (or save labor and have customers fill their own drinks) and now everyone does it. At that point, straws were just something that was expected.
Can you prove this at all? I’m seeing White Castle offered free refills in the early 60s and plastic drinking straws didn’t become popular until the same time period.
I worked at McDonald's for several years in the 1980s, they did not do free drink refills (coffee excepted) at that time. As I recall, most other restaurants did the same.
At some point restaurants realized they could offer free refills as a competitive advantage, (or save labor and have customers fill their own drinks) and now everyone does it. At that point, straws were just something that was expected.