They do, actually. That’s why the pet RNG is programmed in the way that it is. It is working exactly as the devs are intending, just as Salty has mentioned earlier in the thread.
The goal here, as Neritar is in the right ballpark, is to induce players to spend gems on pets to mythic them. RNG is the natural roadblock in achieving this outcome. Players want specific pets to appear, while RNG tends to prevent specific outcomes (a desired pet) from occurring, especially when drawn pet rescues are not removed from the draw pool and each drawn pet rescue is an independent outcome. As the pet pool becomes more and more saturated, drawing a specific pet rescue will become increasingly harder and harder to obtain. As shown on the graph at the Wikipedia link, for every pet that is added to the draw pool, the difficulty in pulling a specific pet increased in a greater than linear fashion.
It’s a variation of Coupon’s Collector’s problem, except that instead of needing to draw a pet rescue once, players will need to draw that pet rescue 16-17 times (on average, plus/minus RNG on drawing pets from baskets) and fully clear it to avoid spending gems on pets. As the pet pool increases, the odds of a specific pet rescue occurring naturally in a reasonable timeframe (which are already poor) worsen considerably.
And, of course, the streakiness of the RNG algorithm used doesn’t help matters at all.
Dilbert on RNG (not directly pasted because of copyright reasons).
As Lando Calrissian famously quipped, “This deal is getting worse all the time.”