Because they know that they're telling lies!
Article from Nation Cymru here:
https://nation.cymru/news/ban-on-politicians-lying-law-shelved-despite-cross-party-support/
The man who put it forward is Adam 'transwomen are women, no debate' Price, former leader of Plaid Cymru. The proposal wasn't passed because it was believed that it might disrupt the Senedd reform Bill which will seek to sneak self-ID into legislation.
Lots of rumours here in my bit of Wales that Plaid, which Labour relies on for a majority in the Senedd, is forcing Labour to persist with a full-on gender ideology/ trans rights agenda when there are signs that Labour are concerned it's a vote-loser.
Scotland, you have a rival for the most batshit, tribal and untrustworthy government in the UK.