It's not.

2.4GHz suffers from less attenuation (it penetrates walls better) due to the longer wavelength, but the cost is a reduction in data rates. That's why it's seen as a legacy standard these days..it's low(frequency) and slow(data rate). But I'm not saying you should disable it on your home router though, it's fine as a fallback (maybe split your SSID's though).

In Enterprise deployments though, it's all about coverage with 5GHz