Because now your inflexible base-load has increased. And while spreading generation over a wider area helps, it rapidly reaches limits (unless your power grid extends close to the equator).
In a country where heating isn't yet electrified, it's a way to reduce fossil fuel use and carbon emissions (the ultimate goal) without necessarily reducing the fossil electricity production. So even if it doesn't solve Dunkelflaute alone, it's a part of solving the climate and energy crises.
This is not _too_ bad in itself, using gas for generation and then powering heat pumps is more efficient than burning gas for heating. But the capital requirements for new power plants will cement Germany's dependence on fossil fuels for at least another 2 decades.
It's a mess.