I must have missed where you mentioned how those factors are unique to Canon, and do not apply to Sony or Nikon.
I wonder if you're trying to be snarky but I'll assume it's an honest question.
The simplest example I can think of is if firm A is basically making zero profit: the corporate tax differences in different markets don't matter as corp tax is due on profit. No profit means no taxes, allowing it to set prices more similarly everywhere. Firm B, that is making profit, has to therefore consider something firm A doesn't. What we'd expect to see is firm B both more interested and more able to price competitively in a region with low tax, and attempt to grow market share there, while in a high tax region, firm B would have higher prices, to recoup more similar net profit per unit after tax, even at the cost of diminished market share. If this isn't clear, take it to extremes: imagine an extreme scenario where a certain country has a corp tax rate of 100%. A profitable company might not bother selling there at all, and leave that market to companies that aren't operating profitably.
Different firms will be locking in their FX rates at different times and for different horizons. One firm may have done so at when the yen was at 100 for 5 years. Another firm may have done so at 140 for 2 years. If you want more details on how this works I can go into great detail.
Different firms have different corporate structures that give them different tax rates in different markets. Maybe firm A has set up an import company in Ireland and books their profit there and pays low Irish tax rates, while firm B hasn't and pays far higher German tax rates.
Or firm A's lawyers have cautioned it AGAINST setting up an Irish profit-booking entity on the grounds that the EU or the US may determine it's tax cheating and land a fine on firms doing it while firm B has decided it's totally legal and is paying lower tax for this reason. In fact one may even be paying off some sort of fine while another isn't.
Or if you're looking at the UK, maybe one firm has had a UK corporate entity for decades, and now that the UK has left the EU has dusted that off and is using it efficiently, while another doesn't have such a firm or has had the cost of setting up such a firm only since Brexit. Maybe that entity isn't set up efficiently yet. Or contrarily, there may be some special tax rates available now that weren't available before. If you're in the US you've seen this when a state offers a 10 year tax rebate to a company to set up a factory there. Other countries have special economic zones whose rules vary over time and some companies were able to take advantage of them and some didn't.
Some countries have preferential import duties for certain countries. If firm A is making lenses with parts from Mexico and firm B is making them with parts from China, firm A pays lower import duty to the US due to the USMCA (the new NAFTA) allowing freer trade between the US Canada and Mexico. If you're interested especially in UK/EU, these countries are often very preferential to their old colonies. I don't know that this would be a factor in lens/camera manufacture but it's been a problem for decades in the banana trade.
Some firms may be running their UK help desk in the UK at high UK prices while another firm is doing it in the Philippines.
If you're being like AlanF and setting the bar at me having to PROVE why prices differ, you're setting the bar too high. Even industry analysts who know every public financial detail of the various firms' operating structures will not be able to know for a fact exactly why prices are set like they are. An analyst might even have noted an "official announcement" explaining the pricing but even such public communications, while they have to be true, may be far from the whole story.
