I don't believe he ever left…
If you look at his background…1st in his class at West Point…then politics (Kansas Senator)…then Trump taps him first to clean the C_A then move on to the Deep State dept…you don't entrust that job to just anyone…while he hasn't been featured in the news much since the 2020 election loss…he has still been active…just low profile:
U.S. former top diplomat Pompeo arrives in Taiwan, calls it 'great nation'
https://www.reuters.com/world/us-former-top-diplomat-pompeo-arrives-taiwan-calls-it-great-nation-2022-03-02/