Should my resume say why I left each job?

No. A resume lists your roles, dates and achievements; it does not state reasons for leaving, whether you resigned, were dismissed or left by agreement. Employers do not expect reasons there, and adding them uses space and can raise questions that are better answered in conversation.

What the resume shows:

• Job title, employer, location and accurate start and end dates.
• Your responsibilities and results.

Where reasons are given:

• Application forms that ask "reason for leaving". Answer these truthfully and briefly.
• Interviews, when the employer asks.
• Sometimes in a cover letter, if a short note helps explain something unusual, such as a planned relocation.

Leaving reasons off the resume is not hiding anything; it is the normal format. The important thing is that what you say on forms and in interviews is honest and consistent with your dates.