What About The Voluntary Offerings?

In our davening we say מפני חטאנו גלינו מארצינו וכו' ואין אנחנו יכולים לעשות חובותנו - Because of our sins we have no beis hamikdash and cannot bring our obligatory offerings חובותנו.

How many times have we said that and not thought - Well, we can't bring voluntary offerings either?? So why do we only mention the obligatory korbanos?

[Rav Baruch Mordechai Ezrachi Shlita]