'Cause we all have Hebrew names. He was probably named for someone who also had Yitzkah (Isaac) as their Hebrew name.
The English translations do change over the years. Two of my cousins and I are named for a woman named Yetta, who is great-grandmother to all of us. None of the three of us are named Yetta; we are Jane, Jamie and Janet. But we probably could have been Yvette, Isabel and Jessica. Most parents go with something in English (or whatever their native language is) which sounds kind of similar. I, H, J and Y are often shuffled around, semi-interchangeably (there is no J sound in Hebrew) when it's time to name a baby.
For English names pulled straight from the Bible, the relationship is a lot easier to follow, e. g. Rifka for Rebecca or Adom for Adam.