This isn’t an issue with lyrics, but with the Vertical Justification of the staves and systems on the page.
Dorico is (rightly) spreading out the music to fill the page. It does this by starting with the Minimum Gap values in Layout Options – in your case, the gap between a Staff to a Staff group, and the gap between systems. It then either stretches just the gaps between systems, or between systems and between staves, depending on the Vertical Justification percentages.
I’m guessing that you want a smaller gap between the vocal line and the piano. You can force Dorico not to stretch the gaps between staves at all, by making the 2nd Justification percentage a much lower value.
This means Dorico will never stretch the gaps between staves, on the gap between systems.
Alternatively, you could just increase the Inter-system gap:
… and reduce the gap settings between staves. Dorico will still stretch everything, but give more weight to the gaps between systems, and less to the gaps between staves.
By default, Dorico stops stretching the gaps between staves when the page (frame) is above 80% full. I’d guess that this is happening on page 1, which, it could be argued is too tight.
As with all things, there’s a balance to be struck between too much white space between the staves, and too much white space between the systems. The latter is just as bad. For some reason, a lot of Sibelius scores suffer from massive white spaces between systems on the page.