Celta Vigo forward Aspas, 30, scored 22 goals in La Liga this season, while Morata netted 11 in the English Premier League.
Former Real Madrid striker Morata joined Chelsea last summer aiming to become a key player at Stamford Bridge and cement his place in the Spain side, but poor form and injury problems saw him fall behind Olivier Giroud in the second half of the campaign.
"I spoke to (Morata), but it's a decision that the coach had to make. Alvaro is out and so are a lot of other very good team-mates," Aspas told reporters.
"(Mario) Gotze scored the goal which won the last final (for Germany in 2014 against Argentina) and he is not going to the World Cup. You have a bad season and another team-mate will have the opportunity to be here (instead)."
Aspas has scored four goals in eight appearances for Spain, making his debut in 2016 under Lopetegui when he scored in a 2-2 friendly draw with England as a substitute.
"I've worked to be here since the first day with a lot of hope," added former Liverpool striker Aspas. "I came into the squad because of an injury to a team-mate and (Lopetegui) has given me the chance to keep coming.
"I would like to start all the games, me and anyone else in the squad, but it's to the coach's virtue that he thinks that I can help the team with just a few minutes on the pitch (as a substitute)."
(Editing by David Holmes)
