Why did it fail?

because everyone hated the theme song

They churned out two seasons of utter derivative crap and hoped it would suffice in entertaining the slow-witted, hard core fans.

Trip and Reed trapped in a shuttle pod. Trip and alien woman trapped on a ship. Archer and Reed trapped on the hull of the ship. Mayweather and Reed trapped on an asteroid. Archer and Trip trapped on an alien prison ship. Trip and alien trapped on a planet together. Archer and T'Pol trapped in cell. Archer and Mayweather trapped in internment camp. Archer and Trip trapped on desert planet. Crew trapped in catwalk.

By the time they realised that shit just wouldn't do, it was far, far too late.

The show actually got very good in season 4, but seasons one and two were pretty ordinary. But TNG, Voyager and DS9 all had pretty bad Seasons 1 and 2.

(1) Having a pop theme song instead of an orchestrated composition seemed like a gimmick to draw in younger viewers. At first I thought I was listening to Rod Stewart. The music should have reflected the grand adventure of the early exploration of the universe. (2) Being a prequel in and of itself meant that everything about the show would be scaled down from the previous four shows set further into the future. This was a built-in handicap that may have turned off some fans who were expecting the same level of slam bang that the previous series offered, though that's not to say the stories couldn't be as relevant or entertaining with some decent writing. (3) Considering that the template for Vulcans was Nimoy's half-human Spock, they at times came across as rather emotional for full-blooded Vulcans, though I admired Jolene Blalock's underrated stoic persona as T'Pol. She epitomized the true Vulcan nature and only drifted into new emotional territory after her character was exposed to a substance particularly toxic to Vulcans. (4) Though time travel is arguably is one of my favorite themes in speculative fiction, it raised all sorts of issues in this series, such as what happened to all of that juicy information about the future that Archer had in his possession. The questions raised about contamination of the timeline are endless. Perhaps they would have tackled those issues in the future seasons that never manifested. How ironic. (5) Technology issues: transporters but no tractor beams? Really? Having transporter technology in that early time frame seemed like a real stretch for me. I could live with the idea that they would have to rely on shuttles to get around for the short hauls. I could even live with the idea of lasers instead of phasers or even a high-powered rail gun which could pack a mean punch in the vacuum of space. Remember, the Old West wasn't tamed with M-16's.

A terminal lack of originality.

I must have been in a different space when this was on. I'm fond of the original, Next Gen and Voyager. I didn't even mind Deep Space Nine when it happened to be on. This flew right by me, and I'm not sure how I feel about Bakula. I saw him in one series (Quantum Leap) where I thought he was charming, but now on NCIS: New Orleans, I'm not sure. Him putting on a little Louisiana lilt in his voice seems silly. And he's got some odd name, like Army. Actually, I wanted to have some facts here, so his name is Pride, like Charlie Pride, I guess.

(Episode 36) Truth OR Myth? Star Trek: Enterprise, Was It Really That Bad?

https://www.youtube.com/watch?v=nnHOQUMwERE&t=1s