It's the nozzle. Let's suppose you really wanted to design your own nozzle... you could use something like MUMPS, which is $5,800 for 15 dice, plus 100 for each additional. You have to wrestle together 15 people to pay 400 bucks (or 20 to pay 300, and so forth) for a printhead that probably won't work. Figure it'll take several iterations and everyone needs to be in for thousands and thousands of dollars.
It's doable but only among a group of very wealthy hobbyists.
People with this kinda money typically gravitate towards high vacuum projects and microwave electronics