It's actually going to raise questions as to why the EU are A-OK with this now when a possible interpretation of associate membership is it's what Cameron was trying to negotiate the UK into when complete inflexibility on the EU side triggered the Brexit referendum.

All depends on what an associate member is of course.

Why is the EU obligated to treat every country the same way? Canada presents different economic opportunities and challenges than the UK. Or, if you want to say it was due to politics, who was bashing who?

The UK already enjoyed a large amount of concessions as a full member. The rest of the EU was right not to give in. Also, game theoretically it's of course more important to not make leaving (or threatening to leave) the union seem too lucrative. No such problem in negotiating tighter integration with nonmembers (and in retrospect, many of the old WP countries should've joined as something like associate members at first…)

I don’t think Cameron did much serious negotiation on this front. He resigned the evening of the referendum results.

It was a deliberate choice by his successors to pursue a hard Brexit. A softer Brexit was always possible and likely would have been more acceptable to the EU, as it would have had less financial impact and disruption to trade.

>inflexibility on the EU side triggered the Brexit referendum.

That's a bit of a stretch

I missed the part where the UK was willing to give up all veto and voting rights and still have freedom of movement.

Both of which Canada is ok with.

I mean, not really, since the UK was trying to renegotiate an existing deal (which they profited from for decades) towards a deal that would favor the UK more than the EU and would trigger an entire blow-back of other member-states wanting to renegotiate on their EU responsibilities without losing the advantages that this deal brought, whereas the deal with Canada is a new deal where the EU gains better trading and less dependence on the US and Canada gains better trading and more security if their next door neighbor falls apart even further.

The UK renegotiation was a net loss for the EU, this Canada deal is a deal where both parties gain something.

Also, the Brexit referendum was a campaign promise of David Cameron that was going to trigger if his conservative party won the 2015 general election. Sure, the relationship between EU and UK had strained over the years, but trying to pin this on the inflexibility of the EU feels a bit misdirected.

The UK wanted to maintain its veto over all EU matters (cake and eat it too).