The supernatural virtues, whether theological or moral, cannot be acquired through nature or natural human action.
They must be infused into man's soul by God. The infused theological virtues of faith, hope and charity, have God Himself - as He is in Himself - for their immediate object. Since this Object - God as He is in Himself - is beyond the natural powers of man, the virtues which unite man to this Object are also beyond man's powers to acquire. God Himself must give virtues to man (My Way of Life, p. 243).Sola gratia indeed.
When God by his grace gives the Protestant the gift of faith - which he exercises - that is sola gratia. But when God by his grace gives the Catholic the gift of the theological virtues...that is "obviously" the work of man. Sure. The source is the same, and both result in the exercise of the gift by the recipient (the Protestant believes - which is a human action; the Catholic exercises the virtues - which are human actions).
I do not understand why one is (in some people's eyes) sola gratia, and one is not; I merely report.