# Why does the stability of hydrides decrease down the group in nitrogen family?

Why does the stability of hydrides decrease down the group in nitrogen family? Does this have to do with the fact that $\ce{NH3}$'s $\ce{N}$ is hybridised ($\ce{sp^3}$) while the rest of the group prefers unhybridised central atom for hydrogens leading to steric replusion in $\approx 90^{\circ}$ alignment of $\ce{H}$s?

Other possible explanation:

Perhaps, the orbital overlap order is: $\ce{2sp^3-1s > 1s-3p> 1s-4p>1s-5p> 1s-6p}$ which leads to greater stability of $\ce{NH3}$ over the others.

As far as overlapping is concerned the bonds in the hydrides are - $\ce{2p-2p}$ up to $\ce{5p-2p}$.