why use Dextrose instead of sugar?!

Dextrose is pure glucose and table sugar is a molecule made of one glucose and one fructose. Yeast's preferred food is glucose, so the dextrose is eaten easily and turned into alcohol and carbon dioxide. The yeast can break down the table sugar, eat the glucose, but then it must alter the fructose and turn it into something it can eat. That process is complicated, and the yeast will only do it as a last resort, and the metabolic byproducts of that conversion process can produce off flavors in the final product. Best to stay away from table sugar when brewing beer.

It's a higher potency sugar. The higher the sugar content when you ferment beer, the more food there is for the yeast. This makes the yeast get freaky (that's right freaky) and produce more alcohol in the finished product. It's also easier to control as an ingredient than convventional sugar, as it is available as a powder and a liquid. I think it f*cks the flavour up though. Higher alcohol content beers are usually funky tasting.

Beer was my life for a great many years.

You could use table sugar and there are some recipes that specify adding a small amount of brown sugar. However, table sugar gives your beer a "winey" taste. You don't want that.

Yeast converts dextrose to alcohol first, with more ease, so it reduces the risk of a stuck fermentation, but I think it is a pretty small risk anyway...

dunno