I don't recall that there was ever anything inherently wrong with using tables for layout, except that it was a misuse of tables so we were told it wasn't "semantic". Thus you had years of people asking on forums how to emulate tables using a mess of floating divs until flexbox/grid came around. In retrospect, tables are also clearly incompatible with phone screens, but that wasn't really a problem at the time.

One, it made the code unreadable and impossible to maintain properly, especially since most of those table where generated straight out of photoshop or whatever.

Two, it was an accessibility nightmare.

At least modern grid design fix those