RCOOH and H2CO3

consider the first delocalization.
for both hydrogencarbonate ion and ethanoate ion, both of them have TWO oxygen atoms for delocalization (resonance). [the third oxygen in hydrogencarbonate ion is binded to H, making delocalization onto this oxygen less feasible.]

apart from that, consider inductive effect. the third oxygen (H-O-) in hydrogencarbonate ion has electron-withdrawing effect, reducing the electron density in the resonating system. methyl group in ethanoate ion, however, has electron-donating effect, increasing the electron density and strengthening the basicity, in turn weakening the acid.