It's not necessarily popular
now. If you sift through the annals of anime history, you'll find many many mediocre or lousy series with terrible outsourcing. The most famous one appears to be episode 4 of Lost Universe... aka yashigani. (You can find clips of it online to see how bad it is.)
They... tried to
rectify it. A little.
Don't forget Mahou Sensei Negima (although that was corrected because there were a lot of people who complained; whereas I think people just forgot about Speed Grapher.)
This season's yashigani is
Musashi Gun-dou. うおっ、まぶしっ!
Though frankly speaking Ergo Proxy's bad animation wasn't as bad as Speed Grapher's. It's a real pity because Speed Grapher, IMO, had the best potential out of almost all the Gonzo shows there are - it really deserved the good production values that things like Gatekeepers and Last Exile received. But no...
This is what really makes me hate Gonzo. Asses. Can't recognize talent (like Masashi Ishihama)when they see it because they suck so much. Grrr.
At least the creators managed to get some good stuff out: re the first episode, episode 22, and the Real OP (which is sooo coool.)