What is HTML?
An HTML table is what a web page shows and what a browser copies to the clipboard. It carries structure a plain grid cannot - merged cells via colspan and rowspan - which is exactly the part a converter has to expand back into ordinary rows.
What is TSV?
TSV is CSV with tabs, and the swap removes CSV's worst habit: prose is full of commas and almost never contains a tab, so fields rarely need quoting at all. It is what you want when the data is text-heavy and the quoting keeps going wrong.