In order to protect its genome from the mitochondrial genome, the host cell had to evolve the nucleus and possibly also sexual reproduction. Once that's done, it works just as well for the chloroplast.
The nucleus is also considered a potential candidate for endosymbiosis [1] and I'd really love to see some actual evidence for your claims at some point instead of just vague handwaving
(1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4571569