cost is too high, or they already are doing it.

"Good wifi" is becoming more affordable because of competition (thanks Elon). If the cost of wifi is built into the price of every ticket then why should people not using it have to subsidize those who do? Even ULCCs are starting to offer it though.

For meals, the loading, preparing/heating, delivering, cleaning, insurance, and jet fuel cost will always be more expensive than a nice restaurant + tip. Your own food is much cheaper, tastier, and safer, just not heated unless you bought it at the airport but that's not cheap either. Most airlines don't charge for airport food being carried on. It's possible to carry several days of good food and snacks between a carry on and a personal item while still carrying two changes of clothes, three sets of underwear/socks, spare shoes, two laptops with cords, spare large battery to charge phone/computer if stranded, and a little room leftover. I do it every single flight 4+ times/month.

Loading back to front sounds nice but then the people with more expensive tickets don't get the extra 20-25 minutes to settle in and get their computers etc set up or finish their business. They would also run the risk of there being no space for their carry on when they finally board. It's not unusual for full flights to run short on space for carry ons requiring some people to check their carry ons with all the associated and statistically significant risk of lost luggage.

Enforcing carry on sizes is already done by most airlines at the gate. It's a good idea though.

Charging for specific seats is fine because then the people who don't care where they sit can save money. It lowers the cost for my ticket because I fly solo and don't care where I sit. Why should I pay for others who do care? Where it counts, all airlines - even ULCCs - will seat children next to an adult. Fwiw random seating is a good justification to not have to sit by someone you don't want to anyway for several hours.

Checked bags are expensive weight and space wise because their weight costs jet fuel and their space costs space for carrying cargo (many passenger flights carry cargo too). The cost must be build into the price of the ticket. Why should I pay for something I'm not using?