Perhaps it's because the vinegars can settle out, so you want to shake the bottle? You can't do that with a tube.

My supermarket here in the Netherlands has most condiments in such tubes. I like them in outdoor situations, like when going camping or in the park. They're more messy than bottles or jars when used on a table, which is why I think that packaging is relatively niche.

It's probably a sizing issue, given how much ketchup gets used, you'd need a lot of toothpaste tubes, and making them huge would lead the the same issues as you get with other containers.

I thought the article's reminiscing a bygone era now that the plastic bottle have sort of won?

I find them perfectly adequate to be honest, the full on red ones, or the upside down supermarket types...

Hold the bottle parallel to the plate and tap it gently against your other hand. The ketchup comes out easily. It’s only hard to get out if you hold the bottle upside down (like you would with anything else). ;)

It does, you’re missing “ketchup in plastic pouch” google search.