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 XML?
XML is the verbose, strict ancestor of most structured data formats, and it is still what enterprise systems, publishing pipelines and older APIs exchange. Tabular data in XML is usually a repeating row element with one child per column.