Low volatile nature of ${\mathrm{H}}_2{\mathrm{SO}}_4$ is due to

The volatile nature of compounds depends on the intra-molecular forces of attraction between the atoms. In compound, ${\mathrm{H}}_2{\mathrm{SO}}_4$  there is hydrogen bonding present and thus its volatile nature decreases which makes it less volatile. The hydrogen bonding exists between Hydrogen and oxygen atoms in ${\mathrm{H}}_2{\mathrm{SO}}_4$  molecule.