It's a fairly established approach to campaigning for change.
If it's a change that will have lots of voices resisting it from different directions, you neutralise as many of them as you can before going for the big change.
If you go straight for abolition of the Lords as is, whatever political party is driving it has the CofE, the hereditaries, the cross benches, and probably two other political parties opposing it as the main groupings of vested interests.
The life peers are the big change. That would be the last part to go in any reform.
The remaining hereditaries are a bit of a joke and wouldn't have much credibility in a public debate. Still, if there was an opportunity to get rid of the last ones (or even get more minor reform that they don't get replaced as they die out) then that would reduce the noise. The previous Lords reform on hereditaries has already done a lot of the work here in rendering the remaining ones a lot less relevant in public life.
The other minor group are the bishops, who would create a separate centre of gravity from the life peers in any public debate and would make the campaign more challenging. The CofE is a well-resourced, well-funded operation that is accustomed to issues-based and political campaigning, and would be more of a challenge than the hereditaries. Taking the CofE out of the equation earlier would make the final campaign a lot more straightforward.
So yes, minor reform as a precursor to major reform can make the major reform easier and more likely.