1. Insufficient relevance: If the internship experience is irrelevant to the requirements of the position you are applying for, it can be omitted from your resume to avoid being too lengthy.

2. Long time: If the internship experience has been a long time now, the requirements for the job application may not be very important or relevant, so it is omitted.

3. Resume length limit: Resumes usually need to show personal information and experiences in one or two pages. If you have a lot of internship experience, you may exceed the length limit of your resume and need to filter and omit it.