As Mkali says, Thisbe's originally Greek, all right - Shakespeare took the Pyramus and Thisbe story from the classics, names and all.
Not many languages make a th sound - English and Greek spring to mind! So it's likely that people living in, say, Germany would have dropped the H which they wouldn't pronounce anyway, and arrive at the Tisbe spelling that way.
This probably wouldn't happen now - so much scholarship has gone into researching the historically accurate sounds of words, and this is reflected in our versions of the old stories. I grew up with the knowledge that Ulysses
met a sorceress called Circe
, but kids today learn that they were Odysseus
and Kirke all the time!
Which is cool - but I bet the lad in question wouldn't recognise himself as oh-DIS-ee-is; nor would I know what he would have answered to ...