Because those states are doing it through ballot initiatives and Virginia has really restrictive measures when it comes to those.
Virginia does not allow the initiative and referendum process, so all ballot measures must be referred by the legislature. The 2018 state legislative session ran from January 10, 2018, through March 10, 2018, during which time the legislature had the power to place legislatively referred constitutional amendments on the ballot. Legislatively referred amendments can be proposed by either house of the legislature and must be approved by a simple majority of members of both houses during two consecutive legislative sessions. Once on the ballot, amendments must be approved by a simple majority of electors to be enacted.
More broadly speaking, Republicans won a trifecta at the state level in 2010 which allowed them to redistrict the state very favorably for them. This practically locked in their advantage at the state house for the next 10 years. When you draw districts in a way that leaves no threat to your majority and your only concern is being primaried, it tends to cause the party in power to shift further down the ideological spectrum. For example, last year Democrats won the state house popular vote by 10 points and still failed to take the house of delegates. That's insane.
Beyond 2020, though we're going to see the state's districts be much more fair. They could even favor democrats if they manage to sweep the trifecta in 2019. Expect to see most of that regressive shit swept away once Republicans are forced to compete for Independents to win.