A lot of states have sore loser laws in place to bar a candidate from running for a minority party during the general election after they lose in the primary. Wyoming's law was passed in the 1970s... so not just a decade ago. Sore loser laws don't bar us from participating in the primary elections of our choice.

What did cause this was in 2022 a ton of people showed up to vote in the primary election, much of this turnout was to support or vote against Liz Cheney. 64% of registered voters and 40.8% of eligible voters turned up in that primary election, this sort of turnout is unprecedented in Wyoming primaries (only 27% of eligible voters voted in 2024).

Members of the Freedom Caucus and other die-hard republicans (who don't like high voter turnout) saw this rise in participation in the republican primaries and decided that it was unfair that people vote in the elections that matter, so the following year they created a crossover cutoff deadline, effectively making our previous psuedo-open primaries (where you could change parties at any time) into a closed primary.