The thing about Brexit is, you have to have a border between the UK and the EU somewhere. If you put it in the English Channel, you effectively push the Republic of Ireland out of the EU without its consent. If you put it on the border between Northern Ireland and the ROI, you drive up the cost of doing business between the two and make political cooperation between them more difficult. If you put it in the Irish Sea, you imply that residents of Northern Ireland aren’t really part of the UK, and that Northern Ireland is destined to be reunited with the ROI, regardless of the wishes of the Protestant majority. It’s a mess.
The EU will never, and should never, agree to the border in the English Channel. The British government, having agreed to the Irish Sea border in order to get the deal through, now wants to renege on it. That leaves the land border as the most plausible alternative. When it is all said and done, that’s where it will go, notwithstanding the down sides for everyone.