Despite the wizarding community's best efforts in protecting the muggles without revealing themselves, they were getting closer and closer to extinction every day. Wizards and witches were safe from any harm due to their magic capabilities, and therefore used shields instead of walls and wands instead of blades.
The Titans were a terrible foe; ones that even experienced wizards had trouble dealing with. Not many spells and curses worked against them in the same way they would work against humans. The Killing Curse was useless; only cutting spells did any real damage. Witches and wizards who had a lot of talent could cut right through; others had to cut from behind. Even so, they were always safe within the shields and barriers they created.
Unlike the muggle's walls, the Titans had no chance at breaking them. Any attempt at destroying the shields only caused harm to whatever creature was trying to bring harm to it. There was nothing stopping people from disapparating inside, so there was no reason to allow anything in or out.
Needless to say, they had it within their power to protect the muggles from the Titan threat but made little effort in doing so. It would put them in harm's way for sure; if the muggles knew about their existence they might attempt to start a war with them. On the other hand, many people believed that muggles would be more grateful than anything.
In the wizarding community the topic of muggles was a tough subject to approach. Some people thought it was wrong to leave them to fight the Titans on their own when they didn't have a strong ability to do so. Others thought it was necessary to assure their own survival.
Many people knew that if they didn't act as soon as possible that the community would eventually forget about the existence of muggles altogether. Perhaps it will be because they were mostly protected from the outside world and only those that wanted to fight the Titans, whom meant no harm to them when they remained in safe areas, would be exposed to them.
Or maybe they'll forget about them because of muggle extinction.