California gained 3.7 million people from 1970 to 1980 and Texas gained 4.3 million people from 2000 to 2010. The reason California gained 7 and Texas gained 4 is because the country was smaller in 1980 than it was in 2010.
I would argue it is slower now because its expensive to live there. That's a guess though. More people would probably rather move to Texas, where you get warm weather and an easier way of life.
California gained 7 U.S. House seats/EVs in the reapportionment following the
1990 census (population changes
from 1980 to 1990, thus "the 1980s" (I can see how the title could have misled you)). California only gained 2 seats/EVs in the reapportionment following the 1980 census. How many million people did California gain (net) from 1980 to 1990? I bet it was more than Texas did from 2000 to 2010.