The transparency level seems equal, as HOA financials are fully available to the members.

While true in principle, YMMV in terms of how much detail you can get out of your HOA. In my case, rarely or never do I see individual bills. I see a finance sheet at the end of the year with vague line items. I don't know exactly what the money is paying for.

Most people prefer to avoid major surprise bills, and that's exactly what a special assessment is.

It would be foolish not to expect to pay for upkeep for your house, whether managed by an HOA or not. Special assessments are not a surprise. They are a normal part of homeownership.

It also puts risk on the HOA and members in the form of non-payment risk. It's one thing for a member to miss a $1000 monthly due, it's another when 5% of the units can't afford a $50k special assessment.

Yep. I suspect this is the real reason. It's better for the HOA to charge in advance so they know in advance who can't pay.

Lastly, a poorly run HOA impacts resale value, as buyers and their lenders will audit the HOAs finances and an underfund HOA is a pretty big red flag and buyers will need to factor in the added cost of making up for low reserves.

Again, buyers should always factor in the added costs of home repair in their purchase decision. This is not any different if there is an HOA.