The tricky part for me is the roots. Placing eggs underground is perfectly normal, so I don't think it needs justification.
What are the roots for?
In plants, roots serve several roles: They are anchors that hold the plant to the ground. They gather water from the environment. They gather secondary nutrients (particularly nitrogen) from the environment. They have a few other roles, but these are the main ones. In particular, roots are not about "feeding", in the sense of gathering energy (and "plant food" isn't food for plants)
So what could be the reason for your pods to have roots? You might want to anchor the pod if it liable to be dislodged. But if the pod has no leaves and branches, this doesn't seem to be a likely concern.
You might want to collect water or nutrients if they are somehow scarce. But why is it not easier for the mother to simply put some of her water and a supply of nutrients in the pod? She'll be putting calorific nutrients in the pod to feed the embryo anyway.
Unless she isn't... If the reason to have roots is to grow plants, perhaps the animal isn't laying eggs, she is planting seeds...
Perhaps her strategy is to plant seeds that grow into plants, that grow roots, and branches and leaves to photosynthesise and grow as plants and which then produce in alternate generations animals.
This looks a little like the alternation of generations that is found in Ferns and cycads, but taken to an extreme:
So the animals are gametophytes. They are formed entirely of gametes, cells with only one copy of the genetic material (unlike human cells that have two copies of each chromosome). They mate and the female produces "pods/seeds" that she plants, or scatters (she might produce only a few or many millions). From these seeds, a sporophyte grows. It is rooted to the ground, it looks like a plant and has no brain. The sporophyte, when it is mature, undergoes meiosis producing eggs (that may be held within its trunk, for example, or scattered) the eggs develop and from the eggs emerge the gametophyte animal that must seek a mate, and may be carnivorous or herbivorous. Perhaps eating the very same sporophyte plants of the alternate generation.
Why did this complex form of reproduction develop? It is a "best of both worlds" strategy. You are a plant for half the time and an animal for the other half. It is hardly less complex than other ways of reproducing - think "placental mammals" for a truly ridiculously complex reproductive cycle.
Some cycads already do this. They produce sperms cells that are tiny haploid animals that actively swim. They are only 0.5mm long, but you can take this model of reproduction to its artistic conclusion and get full size haploid animals.