You can click on the i for a portal and it will tell you the probablity… 1.3%. That means you’ll need about 40 pulls to have a reasonable chance of getting one, but you could pull well over 100 and not get one. People usually post complaining once they reach about 300 pulls.
There’s a wonderful breakdown of this on every HOTM page. You’ll get them. Just don’t bet on getting one every month. Read the entire first post of this:
Suzuna – 5* Ice / Blue - May 2023 HOTM (Hero of the Month) – Initial Release - Player Guides - Empires & Puzzles Community Forum (smallgiantgames.com)