It makes sense to me, and it’s what I’d want to do, myself. But at the same time, there are others who would conclude the opposite, and want to trade Gold and avoid the Euro.
Different people want to do different things, for a huge variety of different reasons.
Many people (perhaps especially among more experienced traders) would want to trade both, partly (as @ProfesorPips wisely mentioned just above) for diversification purposes. With CFD/forex-trading, this is actually a pretty big deal, because all currency pairs are directly or indirectly correlated to some extent.
Some people know a lot about gold and little about the Euro (that‘s the standard “different areas of expertise” answer).
Some people have methods of trading that are highly suited to very volatile financial instruments (Gold); others have systems suited to less volatile ones that maybe don’t even trend unidirectionally for such long periods (Euro).
To some people dealing costs are so important that the significance of having the lowest the lowest spreads and commissions outweighs everything else (and they might prefer the Euro).
There are lots of different reasons underlying people‘s differing preferences, as you can see (I’ve only outlined a few - there are many more factors involved than just those readily apparent ones).
Some people like Lobster Newburg; some prefer Lobster Thermidor; some like Lobster & Courgette Fritters; others like a Lobster Curry (I think it’s usually a waste of a lobster, myself). Some are allergic to lobster but will happily eat crayfish. Some like both but aren’t really allowed by their religion to eat lobster, though they are allowed to eat crayfish. Some (I’ve heard) are even vegetarian or vegan and prefer tofu (baffling, I know - “go figure”).
But in principle, I’m on your side of the debate (if it is a debate?) and would rather trade EUR/USD with a bigger position-size than have anything to do with Gold, myself. I wouldn’t know what I was doing at all, with Gold, and the volatility would scare me off.