1 of 2 things
either 1) like Goku and Vegeta, Raditz's hair as a kid was not 100% the same as his hair as an adult, just "mostly" the same
or 2) Toriyama realized it was ridiculously long and retconned it to be a little shorter.
You've gotta remember, Goku and Vegeta's hair both went through pretty significant style adjustments over the first year or two of each of their introductions, but Raditz was dead so toriyama didn't need to.
Go back and look at Saiyan and Frieza saga vegeta
his hair keeps changing. His face too. By the time the arc ends, Toriyama finally settled on a look.
Compare that to Goku. The way he drew Goku's hair as an adult changed pretty significantly between the first Piccolo Jr fight and his arrival on Namek.
If you fast forward to the end of Z, he's changed Goku's hair again.
Nowadays when he draws EITHER of their hair in color, it's got a ton more volume and spikes than the black and white versions. And even the black and white versions