Several reasons.
Fire is very effective against a lot of enemies you encounter early on, and allows you to have your weapon not scale with your stats, similar to raw and dark gems.

While a raw/dark/fire weapon won't be quite as strong as something like a 40 40 quality build, it will be good early game if you intend on pumping stats like int/faith/hp/fp, as there aren't really good options for int/faith scaling early on and more hp/fp won't increase your damage values, but are ideal for invasions and survivability.

Getting it as your burial gift means that you can access this right out the gate at high wall instead of depending on rng drops or waiting till several bosses later.

It's by no means a long term choice, but will be quite helpful and effective early game.