Why did Hanuman not carry the whole army on his back? What was the need to build a bridge?

Hanuman was very strong, and could also change his size at will. But even if he became as tall as the highest mountain, he couldn’t possibly carry the sheer number of monkeys that were called by Sugreev from all directions. Sugreev commands Hanuman to summon the monkeys, bears and apes from the whole world and he specifically calls out different locations, starting from the Himalayas to the grasslands, forests, caves near sea  and so on. Hanuman sends his messengers, who are high jumpers and fast as the wind, to seek everyone out . The cavalry that finally assembles is as huge as the ocean, with the following numbers with their respective Generals**:


Shatabali brought 10,000 Crore monkeys
Sushena brought 1,000 Crore monkeys
Taara (not to be confused with Tara, the wife of Vali) brought 1,000 Crore monkeys
Kesari brought thousands of armies full of countless monkeys
Gavaaksha brought 1,000 Crore monkeys
Dhuumra brought 2,000 Crore bears
Panasa brought 3 Crore monkeys
Nila bought 10 Crore monkeys
Gavaya brought 5 Crore monkeys
Dariimukha brought 1,000 Crore monkeys
Mainda brought 1,000 Crore monkeys
Dvivida brought 1,000 Crore monkeys
Gaja brought 3 Crore monkeys
Jambavanta brought 10 Crore bears
Rumana brought 100 Crore monkeys
Gandhamaadana brought 10,000 Crore + 110,000 Crore monkeys
Angad brought 1,000 Padmas (10 to the power 27) + 100 Shanku (100,000 Crore or 10 to the power 12 or 1 Trillion)
Tara (this is also a different Tara) brought 5 Crore monkeys
Indrajaanu brought 11 Crore monkeys
Rambha brought 100 Ayuta + 1,000 Ayuta (10 to the power 9)
Durmukh brought 2 Crore monkeys
Hanuman brought 1,000 Crore monkeys
Nala brought 100 Crore + 1,100 monkeys
Dadimukha brought 10 Crore monkeys
Sharabha, Kumuda, Vahni, also even Ramha brought an unknown number of monkeys, probably too many to count

Grand Total: You do the math…
**Refer to Kishkindha Kanda – Sarga 39 for details

Once all the monkeys had assembled, Sugreev summarizes the battle strength of his army to Ram, and tells him the count of monkeys that will be joining the war. He uses the ancient Indian numbering system with units such as Aayuta (1000), Shanku (1 Trillion), Arbuda (1000 Shanku or 1000 Trillion) etc. (Kishkindha Kanda – Sarga 38)

So, it would’ve been pointless for Hanuman to carry all these monkeys in groups because if he drops one group in Lanka and heads back to gather another group, the first group might get attacked and killed by Lankans. But since these monkeys had super fast speed, it made sense to build a bridge so that the whole army arrives in Lanka together.