I have not played since legends was new, but with the latest patch, motivation is building. Partly because there seems to be options to keep the AI off certain designs, and also because I feel like taking full control of my constructors to get a better feel for how many mines are actually needed.
I don't mind babysitting mines until late in the game, and if I control my own mine building, I can try to control where my mines are. For instance entering mine location into the selection of which location to build on.
And if I do that, I can choose to build either a mine with weapons, or cheap star base, at locations that are annoying to defend but needed. And I can also have some custom fuel sources at key locations, that are basically stationary, weaker, resupply ships.
Once tech has advanced past the very start, it does not seem hard to defend mines if a small fleet is parked within one sector distance. And if you control designs somewhat, you can make sure sector defense fleets have fast jump hyperdrives.