Vanilla Marines don't really do razorback spam very well. The other Marine codices have more special rules that make the small units useful.
In general, you're going very minimal on upgrades, so no powerfist. You're already in trouble if you get into CC anyways, so most people don't bother throwing points on a bad bet.
But just for comparison, look at a SW spam list:
5 Grey Hunters, meltagun, Wolf Guard with combi-melta, Razorback with Lascannon/TL Plasma rifle.....178
You get 6 guys, 2 meltaguns, a TL plasma rifle and a Lascannon. Take 4, two with melta and two with flamers, and that's some pretty solid firepower. In just troops, you've got enough firepower to kill vehicles from across the board, really kill light vehicles and/or units with 2+ saves, and you have 4 units that can spread out and claim objectives while your opponent is busy dealing with your more aggressive units like Thunderwolf Cavalry.
Maxing out each squad forces you to take Rhinos instead of Razorbacks, so you pay points in order to lose a lot of your flexibility only to gain a few more bodies and an extra special weapon (which doesn't make up for the ones you lost downgrading your Razorback).
Those 4 units cost ~700pts. 3 units of 9 with a standard and wolf guard with powerfist and combi weapon costs 600pts. Razorback spam gets you 4 rhino chassis, 24 guys with four special weapon, four combi weapons, four lascannons and four TL plasmaguns for 16 special weapons total. Non-spam gets you 30 guys, 3 vehicles, and only 6 special weapons instead of 16, though you do get powerfists.
See the difference?