Former Barcelona centre-back Bartra impressed for Betis in the second half of the 2017-18 campaign, and had been tipped to earn a call-up for this summer's tournament.
The 27-year-old was overlooked, however, despite 'sacrificing a lot' in an attempt to make Julen Lopetegui's selection.
"I sacrificed a lot with this objective in mind, to be able to go to the World Cup, and it's true I took decisions about it, even though it wasn't to be," Bartra told beIN Sports.
"What it has done is made me into a better player than I was a year or two ago, although when you don't reach your goals and the success you want then you have to move on.
"There are some great players in the Spain team, spectacular, who have made it a great year. They are the elite and I wish the national team all the best."
Bartra has made 13 appearances for the Spanish national team.