I've worked for a dozen different companies (contractor) over the past 10 years as a backend engineer and have never been faced with oncall. Neither have my permanent employee colleagues. In many cases we had no direct access to production environments as that was managed by separate teams. In the one startup I worked at, it was so early stage that there were only ever a half dozen users, and the CTO handled any issues that popped up over the weekend.
The type of companies that had dedicated teams for maintaining live environments included big banks, government departments, insurance companies, large healthcare companies.