“Why do I have to quit using my e-cigarette before my surgery? Isn’t this just more bias against smokers for no reason?”
To start from the top, smoking is discouraged when you’re going in for surgery because it increases the risk of all kinds of complications, including during anaesthesia, the surgery itself and your recovery. It’s not just about smoking being generally bad for you: nicotine itself (just one of the substances you take in when smoking) causes vasoconstriction, upping your blood pressure, and restricting the flow of oxygen to your tissues. Healing tissues need oxygen because the cells are doing a lot more work, and there’s a heck of a lot going on during the wound healing process.
If you’ve quit smoking using a substitute that still contains nicotine, the same problems apply. It’s not just an abstract bias against smokers or former smokers. I doubt there’s many healthcare workers who would tell you that smoking is healthy, but it’s generally agreed that nicotine-containing substances improve things a lot, reducing the amount of tar and carbon monoxide you’re taking in, along with other harmful compounds. If you’re using a substitute for cigarettes, that’s great and your health will improve in general.
When you’re going in for surgery, though, you’re putting your body through a lot. Even if the operation is medically necessary and will improve your health in the long run, in the meantime there are risks of infection, issues with wound-healing, etc, etc. Your doctor is giving you solid advice intended to help you heal faster.
If you can’t quit using nicotine-containing substances for whatever reason, then you should talk to your doctor about it. Maybe they can come to an arrangement with you, or maybe they’ll tell you that they just needed to make you aware of your increased risks. That goes in general. When you get medical advice you don’t understand, try asking the doctor why and what alternatives you might have.