According to the studies I've read, productivity increases when workers are mandated to stop work beyond eight hours a day; are mandated to take their fifteen minute breaks and their hour-long lunch break (and to actually eat a lunch); are mandated to leave work on Friday and take a weekend.
This was demonstrated to be effective even concerning workers who obsess on their job and voluntarily work through their breaks, or into the evening, or over the weekend. Breaks from work are good for everyone.
Productivity also increases when you switch to a four-day work-week (at eight hours a day).
Productivity also increases when you commute less, as we learned with telecommuting during the COVID-19 lockdown.
So why do bosses crunch? Why do they create a social climate that pressures workers to skip breaks? Why do they insist on more than the 40-hour work week? Why do they issue RTO mandates?
Pure vindictiveness. The ownership class resents that their workforce has needs and opinions, and wants them to suffer for it, even when a miserable crew reduces profits and dividends.