Yes, people do lose their insurance constantly when they switch jobs...and then immediately sign onto their new plan. Is the argument that switching insurance plans is stressful? What's stressful is remaining uncovered. Switching plans is hardly comparable to the transition to a Medicare-for-all program.
Unless they lose their jobs. Or change to a job that doesn't offer coverage/start a new business. Or have their hours cut to be >Switching plans is hardly comparable to the transition to a Medicare-for-all program.
Why? It would be a one-time switch. Switching costs would be exactly the same as the switching costs you pay every time you change jobs, except you only pay it one time in your life and you don't have to shop around in some silly healthcare exchange or open enrollment process where you get to weigh which absurdly high premium you want to pay despite deductibles being so high that barely any of your routine health costs will be compensated.
And then there is the joy of making sure all your care providers are covered by your new plan. AND hoping your providers don't drop your plan because of insurance company negotiations.