Why SRB2 if SRB1 itself is capable of transfering NAS messages?

Hi Experts,
I was just reading some basics…
Why do you think SRB2 came into the picture when SRB1 itself is capable of transfering NAS messages?
Is it just to define a low priority SRB for NAS messages?

According to @Jaeku_Ryu (Sharetechnote):

“SRB1 is for RRC messages (which may include a piggybacked NAS message) as well as for NAS messages prior to the establishment of SRB2, all using DCCH logical channel”

http://sharetechnote.com/html/5G/5G_SRB.html

So NAS messages are transmitted over SRB1 till SRB2 is established in 5G.

But the same can be achieved by SRB1, why introduce another SRB?