See the main reason is this.
If I'm Chandragupta Maurya, why would I want to spend vast amounts of money and men forcing the passes through the Hindu Kush, fighting my way across Persoia and Mesopotamia and leaving a trail of dead bodies in my wake? The Persian Empire is infinitely poorer, less fertile and less desirable than India which is why no Indian polity has ever pushed to the West. The only parts of the Persian Empire which approach Indian levels of wealth at the time are Egypt and *perhaps* the Levant and to get there you need to cover all the worthless stuff in between. There's nothing they need and rulers don't just go conquering for the lulz. War is expensive and it had better just the costs.
Alexander of Macedonia was from an even poorer peninsula of a mostly barbarous continent- invading richer Persia made financial sense.
There might be a reason for going into Persia. IOTL, Seleucus Nikator invaded Punjab in about 306BCE. He was defeated and forced to concede all of Afghanistan and Baluchistan to Chandragupta in 304BCE. However, ITTL, let us say that Seleucus and his son are killed in battle with Chandragupta and his (mostly) Bactrian-Iranian cavalry is integrated into the Mauryan army around 303BCE (a little more protracted war).
IOTL, around this time, Antigonus Monophthalmus was the de-facto ruler of Alexander's Asian possessions. He was involved in a full scale war with Ptolemaic Egypt, Cassandrine Macedonia and finally, Lysimachid Thrace-Hellespont. Both Cassander and Ptolemy had been defeated by Antigonus and Ptolemy had lost Cyprus and Cassander most of Greece to Antigonus (and his son Demetrius). All of Antigonus' enemies were uniting and it was to this ganging up that Seleucus was invited to after he had made a treaty with Chandragupta.
However, ITTL, there is no Seleucus for the others to invite, and when the Cassandrine ambassadors arrive in Afghanistan, they find out that Seleucus has already been killed. Instead of returning empty handed to their master, they make the same offer to Chandragupta they made to Seleucus - all of Alexander's possessions east of the Euphrates in return for his aid in defeating Antigonus (originally, Syria was not part of the Seleucid domain - it was promised to Ptolemy. But Ptolemy did not fight and Seleucus after the destruction of Antigonus grabbed it) . Chandragupta is not interested in Persia or Babylonia, but the return of the Greeks to India is a major fear for him. Chandragupta certainly did not want a victorious Antigonus to return to emulate Alexander. Better if he can be contained in Anatolia or Syria, so he joins the coalition. Now the battle of Ipsus goes as IOTL - Antigonus dies in battle, Demetrius flees to Greece, and Chandragupta grabs Alexander's possessions east of the Euphrates.
However, there is one major problem in my scenario. I cannot see Chandragupta's new huge empire lasting longer than a generation. Communications, as they exist, are simply too meagre to sustain such an empire. But do try to guess what the Maruyans could try to do to actually hold their new empire together.
Will it lead to a huge ship building effort in the Mauryan empire as it tries to connect the western Indian coast to the southern coast of Persia, as it struggles to hold itself together? Will the need for a strong cavalry or the riches of Babylonia be a sufficient incitement for the Mauryans to try and hold at least Persia and Babylonia with the Mauryan empire? But to hold Persia at its natural frontiers, it should be the Alborz mountains in the northeast, and for Babylonia it will be the Euphrates. And getting messages to these places, let alone troops and supplies, is a daunting prospect at the best of times. So how would the effort be organised?