I've never been the recipient of cancer surgery or had to undergo this kind of long recovery the author has, but I was a professional nutrition coach in a previous life and I have eaten for weight gain in the traditional weightlifting sense, both "clean bulks" and "dirty bulks" and about everything in between.
I would much rather be 30 pounds overweight and try to lose that weight than be 15 pounds underweight and try to gain it. If you're really killing it in the gym, 4-6 days a week, 60-ish minutes of heavy weight training at bulking RPEs of 8-9, and hitting the numbers of sets you need to be for muscle hypertrophy, eating becomes the worst part of your day. The classic "dirty bulk" of a couple big macs and a non-diet soda for lunch is great for the first few days (maybe) but it becomes a chore very quickly, and it's easily 5x worse when you're trying to eat clean and realize your lunch is going to be 2.25 pounds of chicken breast plus multiple normal servings of rice and broccoli. It's a big part of why people bulking end up eating less healthy foods (the caloric density), and seeming eat all day every day (because they do).