Imagine being so fortunate in life that you can sit on your website for hundreds of thousands, if not millions, simply because you "like the name". That's life changing money for me.
I mean, I really would sell for $10MM. But I think I'd be giving someone a real steal for (much) less. Like, sure, I could use $100,000, but does that mean I should sell a more-valuable asset that I happen to own for that little? If so, why?
To answer that question, ask yourself if you would buy milk.com for $100 000. Probably not, I'd wager. The only reason to not sell is the hope that you might get more for it in the future.
I also wouldn't buy milk.com for $2000. Does that mean I should sell it for $2000?
In any case, there is also a time / hassle reason to not sell: It would mean the loss of the only personal email domain I've used since 1994, and that would make for a _lot_ of updating (and crossing of fingers hoping I didn't miss something important).