Well it's very concentrated, I mean I don't think you'd use it on pizza without diluting it, would you? Wouldn't spread very well and would be a very strong taste, could overpower other things you're putting on top.
Pete does a spaghetti thing (known in the family as Grandad's spaghetti LOL - actually, it's his first wife's aunties recipe!) which uses a whole small TIN of tom puree but since you only use one tin for 4 people (or even more people) it's not really a prob - in comparison to the spag itself ! I dunno what's in one of those tins though, I looked yesterday but we've run out, must remember to get some! I shouldn't think there's much more than 100g to be honest; which between 2 of us is 100% fine.
Not everyone on the forum has to be particularly low carb anyway. It's just easier, and nearly everyone needs to feed the rest of their family. You could spread it thicker one side and divide the pizza with a row of whatever you are putting on it. Mom had to do that with cheese onion and potato pie when we were little as sis didn't like onions!