Tell me what is the reason.
1. Electrum is one of the oldest implementations of bitcoin
2. It has multiple active contributors that are always working on the code to improve it
3. It has no serious bugs
4. It is 100% open source with no hidden shenanigans like some of the other "wallets"
5. It is very easy to use for anyone from beginners to more advanced users
6. It is easy to sync since it is a SPV client and it is fast to sync
7. It has always been quick to implement any new feature that comes to bitcoin (eg. multisigs, P2SH, SegWit, Lightning Network,...)
8. It is one of the first HD wallets that let users only backup a "phrase" instead of having to backup their wallet file every time they create a new address
9. It has a very easy to use cold storage setup by easily pairing the cold and hot wallets.
10. It supports all hardware wallets
11. Electrum builds are deterministic so they can be reproduced, so you can trust the binaries they release even if you don't compile the code yourself