Why has he picked on these 4 women.
Politics. They oppose his policies. Some snippets, all from Wikipedia ... :
Ocasio-Cortez
Ocasio-Cortez supports transitioning to a single-payer healthcare system, recognizing medical care as a human right.
Ocasio-Cortez compared the detention centers for undocumented immigrants at the Mexico–United States border to "concentration camps".
Ocasio-Cortez is a proponent of LGBTQ rights and LGBTQ equality.
Ocasio-Cortez has called for "solidarity with Puerto Rico". She has advocated for granting Puerto Ricans further civil rights, regardless of Puerto Rico's legal classification.
Ilhan Omar
Omar has said she is in favor of the abolition of the Immigration and Customs Enforcement agency.
She supports prosecuting federal officials who have been accused of physical and sexual assault of people in their detention
Omar criticized Barack Obama's "caging of kids" along the Mexican border.
I think this is
the main thing:
In June 2019 Omar was one of four Democratic representatives to vote against the Emergency Supplemental Appropriations for Humanitarian Assistance and Security at the Southern Border Act, a $4.5 billion border funding bill that required Customs and Border Protection to enact health standards for individuals in custody such as standards for "medical emergencies; nutrition, hygiene, and facilities; and personnel training." "Throwing more money at the very organizations committing human rights abuses—and the very Administration directing these human rights abuses—is not a solution. This is a humanitarian crisis ... inflicted by our own leadership," she said.
Ayanna Pressley
During her victory speech following the September primary election, Pressley called out President Donald Trump, claiming he is "a racist, misogynistic, truly empathy-bankrupt man."[42] She aspires to impeach President Trump.
In June 2018, Pressley called for the defunding of U.S. Immigration and Customs Enforcement (ICE), saying the law enforcement agency poses an "existential threat" to immigrant communities.
Rashida Tlaib
Tlaib has said she opposed providing aid to a "Netanyahu Israel" and supported the Palestinian right of return and a one-state solution.
Tlaib has criticized Saudi Arabia's human rights violations and the Saudi Arabian-led intervention in Yemen.
Tlaib supports efforts to impeach President Trump. In August 2016 she protested a speech Trump gave at Cobo Center and was ejected from the venue.
There is lots more. Just politics. They wish to put human rights, compassion and equality before money and oppression. They sound like the good guys to me.