
Hello,
If you create a customer journey and send an email, the email is a marketing email.
If you create a marketing email, you can use your created marketing email template.
This is a by-design feature and process.
You want to create a customer journey and send an email. The email should be official and formal.
However, marketing email template is used for helping to create a marketing email easier and faster. It can be very simple or complex depends on yourself, so customer journey uses a marketing email instead of a marketing email template.
If you want to use your created email template, first you need is to create a marketing email using created email template, and then save and go live.
Later, if you want to use a marketing email in customer journey, you could just create a marketing email directly instead of creating a marketing email template.