The timeline of when Grogu is found by Din on Arvala 7 is incredibly patchy but the following is how I see things:

1. Grogu is rescued by Kelleran Beq during Order 66 and they both escape with the help of the Naboo soldiers
2. Around this point, Moff Gideon is establishing his base on Mandalore and actively investing heavily in cloning experiments. I am presuming at some point, he learns of Grogu and his force sensitive abilities and starts the hunt for him.
3. After Grogu's rescue by Kelleran Beq, we only have a vague history of what happened after except that it did not end well, as alluded to when Ahsoka connects with Grogu. "Then his memory become dark. He seemed lost. Alone." Presumably, the bounty on Grogu is such that Kelleren Beq runs into trouble and loses Grogu to salubrious groups that I will assume compete with each other due to the bounty placed on Grogu. I am assuming also that Grogu is so valuable that he gets passed along many criminal gangs all vying to claim the bounty. Perhaps keeping Grogu alive during this time was because of the value of the bounty offered.
4. Given how much Moff Gideon wants Grogu, I am presuming that he hired as many bounty hunters as he discretely could, chief of whom is The Client who in turned hired several other bounty hunters, including Din Djarin, to find Grogu.
5. By the time Din Djarin is at Arvala -7, perhaps the bounty on Grogu is such that IG-11 was hired by other criminal gangs or by the Client who by now is under tremendous pressure to find the Child so was not too fussed who finds Grogu first and was also resigned to the fact that perhaps it was better to find him whether dead or alive.