Why were all of the tactics necessary for the women's suffrage movement to achieve its goal?

to increase public support.

Explanation:

The biggest threat to women's suffrage movement was the inability for them to create a legislation that allowed women to cast out their votes during the election.

To create this legislations, the only thing that they can do is to increase public support and make the government feel pressured to do so.

Which is why they did series of tactics in order to achieve it , such as gathering the mass to conduct a protest, forming interest group to elect progressive candidates, making appearances on Television, etc.