It's probably because the MultiDoge wallet has not been maintained by the dev for a long time. All Mulribit clones like MultiDoge need a snapshot of the coin's blockchain headers taken by the dev at regular intervals and including in an updated wallet. If the snapshot is very old then the wallet has to download all the headers since it was taken.

There was a contest which paid a bounty to the best lightweight Doge wallet, and I think the MultiDoge dev created MultiDoge to win it, then abandoned the project because he wasn't earning anything more from it afterwards.

The dev's last Github activity was 7 months ago and there were sync issues being reported over a year ago.

https://github.com/langerhans/multidoge

We need a new dev to update the project with a new snapshot if the old one doesn't return.