For early game dominance.
Warrior comes online as soon as you build it. The enemy must get HP before it becomes as effective as warrior which really isn't a good thing lol.
Example
A basic gank combo on WW is pre 6 is...
W get close E AA Qhold E AA
Post 6 you Add R to the end.
The CDR allows you to Q again at the end of R
Lets compare to your 1500 HP (which is slightly generous as this hp is where WW starts to fall off anyway) for 60 on hit damage each.
The AD % of Q is 120 and R is 167 so + 72 and 100 respectively
This is WW burst once built. Most champions are around ~1000 HP when Warrior is first built.
So the additions to the damage portions of the combo is
E AA (+60) Qhold(+60) E AA (+60) R (+180) =360
E AA (+60) Qhold (+72) E AA (+60) R (+100) (We can Add the Q thanks to the CDR or + 72 or not up to you)= 292 or 364
Example Zoe must be level 11 to have 1480 HP if you haven't been using or don't have Warrior by this time you are losing bad, if everyone is going even WW is losing. Anytime before this Warrior outclasses Blood razor more heavily.
The CDR and AD is significant as it allows for your DPS to last longer than it would normally fall off. WW can land less and less AA as the game progresses meaning burst is king. Even your ult is not guaranteed to deal full damage. The CDR and damage also grants sustain surpassing or equivalent to the HP you would've gotten with Cinder hulk thanks to E and Q.
Most of your targets as WW are Squishy and while WW does AA a lot his burst is more important so that the W (you should be maxing) can come online faster and give the ATKSPD that BLDRZ would offer. Dealing 1.2 AA per second is not much worse than 1.5 Unless you've been AA for 4 seconds , by which you are hitting Mundo for some reason and he decided not to move.
Runic Echos will not apply to the AA portion of the equation and ratio deals less damage than AD. 90% on Q no % on R so no it's just worse.
Late game though, yes Blood razor will deal more damage in on paper especially to tanks, but with kiting/team fights and items coming into effect WW wont get a lot of procs off.
I tired keeping it simple sorry, got carried away. It's so that you can win the first 15 minutes of the game and be even with Blood razor till 25 then after that since WW falls off anyway there is no point in having the DPS and Cinderhulk would've been better so you can lock down targets with out dying.