More than 1,100 Baggies fans made the long trip through the snow to Suffolk in the hope of seeing their team reach a League Cup semi-final for the first time in 19 seasons.
And Newton was frustrated the players could not give the supporters what they wanted.
"I have to apologise to our fans," he told the WBA website.
"So many made the long trip here in treacherous conditions and we just haven't performed for them. It makes it depressing because we didn't turn up.
"For my mind, when I was a player, I wanted to play in finals and be as successful as possible.
"To know you're in a quarter-final and you have the ability to get to the semi-final makes it bewildering we had so many poor performances tonight.
"I enjoyed a successful spell at Chelsea, where I played in finals, and tonight I just don't know what the players were thinking.
"Forget all the other trappings, you play football to be successful and try and win trophies so you can look back on your career with pride.
"That's what it's about and I didn't see enough desire out there."