I wouldn't read too much into the polling numbers, Slovenia's parties constantly experience ups and downs. For instance, SAB polled constantly below 4 % for four years until the 2018 elections, when they gained momentum at the exact right time just ahead of the vote and made it into Parliament with slight gains. Slovene polls always have a high number of undecideds and non-voters, it is really annoying the overview in Wikipedia doesn't include the 'party only' numbers.
And from what I read somewhere (not sure how accurate it was tho), it's for similar reasons - the society is split into two camps, there isn't a lot of voter movement within one of them or
between them, but the other one is very volatile. Astatine is the resident Balkans expert here, so he'll hopefully correct me, but apparently there's a divide within Slovenian society that goes back to WW2, where people who would've supported partisans vote for liberals/left and četnik apologists vote for SDS/right.
