Okay. Consider this: Honda Swindon produce around 160,000 cars a year. Its half what it was in the good times. A Honda Civic is about £18k. If you do the maths that is many many millions in revenue. Of that 160,000 cars most go to Europe. Some to the US, a few are sold here. Honda would not give up the millions that they are making on this (comparatively small) production. They would have kept things going were it not for (at least) two things. First and foremost, a new EU free trade deal the UK had no say over which means they can export cars from Japan to Europe. Before there was a 10% tax or tariff and that's why Japanese car firms made cars in the UK - to service Europe. Now they don't have to. That is the big piece here. When the CEO gives this bad news its not technically because of Brexit, it because their trade terms have changed. But had we been party to this trade deal, we would not have given up thousands of UK jobs lightly.
Add on top of that that Honda need to plan for electric production lines, and the uncertainty of Brexit (will there be a hard exit disrupting supplies? see Honda's position on Brexit and the same guys quotes a year before
https://www.bbc.co.uk/news/business-45558424 ) Its a no brainer for the Japanese. Had the UK been in the EU we would not have given up these Japanese car jobs so easily as we'd have been at the trade negotiations. However, in return the EU will be able to sell billions worth of goods to Japan that have been stopped with tariffs on their end. It is estimated that the UK benefit from the free trade agreement with Japan is £3b+ each year in new trade. Outside the EU of course we won't get that. But we can make our own agreement with Japan if they'll listen and talk. It took the EU 4 years to do this deal.
Honda senior management will have been planning this with their PR departments for sometime. Planning what they say, planning how not to damage their brand and standing in the UK. Of course they are not going to be divisive and alienate people by blaming the UK. What a stupid move that would be. Draw your own conclusions. But at least consider some of the details.