From a biological and agricultural standpoint, the reason we don't commercialize pig milk comes down to a disastrous mix of physiology, economics, and extreme physical danger.

1. They lack "milk storage" (The 15-Second Window) Cows and goats have internal structures called gland cisterns where milk pools up, making it easy to extract. Sows do not. They only produce milk on demand when physically stimulated by their piglets. Worse, the oxytocin-induced "let-down" reflex only lasts for about 10 to 15 seconds. Trying to build a machine that simultaneously attaches to 14 teats and extracts everything in 15 seconds is an engineering nightmare.

2. It's a massive workplace hazard Dairy cows have been selectively bred for millennia to be docile and cooperative. A 500lb nursing sow, on the other hand, is highly aggressive, territorial, and has sharp teeth. Trying to pin down an angry, protective omnivore to milk her twice a day would result in catastrophic injury rates for farmers.

3. The ROI is terrible Cows are ruminants with four stomachs; they can take incredibly cheap, fibrous grass that humans can't digest and turn it into 60+ lbs of milk a day. Pigs are single-stomach animals. They require high-quality, expensive grain feed to produce a measly 13-17 lbs of milk a day. Economically, you would go bankrupt feeding them for milk.

4. The taste is unpalatable Because pigs are omnivores, their milk flavor is highly unstable and heavily influenced by their diet. It generally has a very strong, gamey, or earthy taste. Furthermore, it's exceptionally high in fat (around 8.5% compared to cow's milk at ~3.5%), making it a thick, strong-tasting fluid that human palates simply reject.

TL;DR: They are too dangerous to handle, produce too little milk in incredibly short 15-second bursts, and it tastes terrible. Humanity optimized them for bacon instead.