Well after 45 years isn’t that just reflecting what the median voter actually cares about (or doesn’t care about)?
If voters were genuinely willing to expend their political capital, time, attention, energy, etc., to a significant degree on this issue, year and year for 45 years… there’s no amount of party intrigues that could have blocked it.
Don't underestimate the power of divide and conquer.
Over here we had miners, farmers, steelmill and shipyard workers protesting due to similar reasons and for the majority the takeaway wasn't that those industries were in danger, but that the protesters demanded too much, because that's what people with influence said.
Of course there will always be various motivated factions looking to divide and conquer… that’s the baseline background noise in any ruling or opposition party.
And the minimum expectation, to advance any policy at all, is to be able to resist that and have leftover political capital, energy, time, etc., above and beyond.
If voters were genuinely willing to expend their political capital, time, attention, energy, etc., to a significant degree on this issue, year and year for 45 years… there’s no amount of party intrigues that could have blocked it.