Cane sugar is sweeter than beet sugar. It just is. You can compare the two by tasting Silver Spoon, which is beet sugar, then by tasting Tate & Lyle, which is cane sugar.
I seem to recall that beet sugar was hardly used in this country until the 70s', when, if anyone remembers, there was a "sugar shortage", which was an absolute load of cobblers. I worked in a food warehouse and there were never any shortages of sugar. However, this brought forward the idea that with beet sugar we could grow our own in this country and thereby help the economy and produce a much cheaper product. Where have we heard that scenario before? North Sea oil and gas perhaps?