Most of the details don't get explained until later but the goddess' personality is inversely proportional to her physical beauty. Hence, while she looks great she's a human supremacist, judges people based on looks not personality or righteousness (human population noticed this hence to garner more of her favor marriages were arranged by beauty so the men are handsome and the women beautiful,) favors women over men, and busy handling whims rather than responsibilities. Heck, the reason the demons are revolting is because she hasn't been granting blessings or anything since sent MC's parents to Origin Earth is because she felt tired, ordered subordinates not to be disturbed for any reason, and took a nap for 20-30 years.
As for MC's parents they were in love with each other, but because of family and political reasons wouldn't be able to marry so asked the goddess to send them to another world. Not wanting to let them leave she tried to keep them by setting forth some impossible tasks, which they completed, and finally a promise that she could call forth one of their descendants to do a job for her. That and she'd send them to Origin Earth, considered the absolute worst world and one of the few with zero magic. They agreed and she reluctantly sent them over. That's why MC or one of his sisters was required to go. Reason demons are rebelling and trying to take over human lands is mainly because noticed the goddess has been absent for a while, sick of living in the frozen tundra like eskimos with no fertile lands to raise food, and are slowly dying out. Hence they're trying to take over the world so can live and survive with enough resources before the goddess returns and empowers the humans to drive them further into the icy wasteland. The humans are full of themselves being the goddess' chosen and believe that since humans are the supreme species the world belongs to them, can do anything they want to non-human species like murder, and demons deserve either be completely eliminated or die out in a barren, frozen wasteland. This POV is encouraged by the goddess who will always judge in favor of a human over a demon. For example, if during a territory dispute a human brutally murders a demon's family, shows up with bloody hands, and only claim to territory is because he says it's his with a pretty face he'll win. The demon, showing a grieving but neat appearance, documents proving territory been in family for centuries, witnesses, and a boatload of evidence will lose. Heck, she'd probably judge in the human's favor as soon as they show up before her and arrange a bath for the human while ordering the demon beaten and/or killed for defiling the area with his presence.
Also, that blessing she gave him was one that imparted all languages except human to him as another attempt to kill him in addition to the fall and location. Not sure if murder attempts were done half-heartedly or was to kill or harass him in a way that she could explain to the other gods as a simple mistake rather than murder. Reason these were murder attempts is anyone from world MC entering would've died or be in extremely bad shape from any one of them. Language was an attempt as the human mind can't process or handle the stress and amount of information for all languages and likely would've killed him if she hadn't withheld the human language to discourage him associating with humans. The fall obviously because at that great height would've normally killed or severely injured him if he didn't get high stats due to difference between Earth Origin that he grew up in and world entering. Like on a smaller scale of Superman buffing up due to differences between his homeplanet Krypton and Earth. Location another murder attempt as it's as far from human civilization as possible in an area considered the worst except for the frozen poles, most of the indigenous species nearby that would try to kill him like monster beasts, and close to a couple Cataclysm class monsters. Cataclysm class monsters are the ones that require heroes, lots of powerful and high ranked soldiers/mages to just drive off, and can destroy an entire country in a few days.
As for the more favorable hero she summoned it wasn't just one. While MC was being summoned she was able to snatch and meet a man and woman (separately) due to them being very compatible with her (ie looks good but some issues in personality such as believing their way is the only right way and other character flaws such as ends justifying the means.) Their meetings went well and both were deposited in one of the goddess' temples in different kingdoms with clergy told to help them out. For reasons not explained the 2nd summon will appear a month or two after 1st summon, and MC will get dropped in a month or two after 2nd summon.