Here is an easy math explanation of why about 80-90% of the gerrymandering comes from the GOP. To enact an extreme gerrymander, one party needs to control both the legislature and the governorship. For the 2010 redistricting, the GOP (after the tea party wave) had complete control of 40% of House seats, while the Dems had control of only 10%.

So even if they were as antidemocratic as the GOP, the best the Dems could do would be 20% of the gerrymanders. But some large Dem states (as well as some smaller GOP states), namely California and Washington, use an independent commission that does not do extreme gerrymandering (although both sides complain about equally about the maps).  As of June 2017, independent redistricting commissions existed in six states – Alaska, Arizona, California, Idaho, Montana, and Washington.[https://ballotpedia.org/Independent_redistricting_commissions]

Of the top 10 gerrymandered states, 9 were done by the GOP and only 1 by the Dems (Maryland). See ” The Top 10 Most Gerrymandered States In America“.
Of these top 10, the 9 GOP states have gerrymandered 106 House seats to only 15 seats for the Dems.