Hi,
In one word because its lovely.
If I want to explain I should say:
1-Its small and fast.setup,compile or anything in Delphi is kind of slow but in Lazarus everything is fast.
2-Its free and open source,Very good reason!
3-Its cross platform.Yes Delphi works in MAC and compile for iOS and Android but not Linux and Delphi mobile apps are slow again.Also I want to write server apps and with Delphi I don't know its possible or not but Im sure its not as easy as in Lazarus.
4-Here you find really good libraries that comes form passion of their developers.Like BGRABitmap.you cant find things like this in Delphi world.
5-Its more geeky.You can do more stuff in more devices.From a server to a mini computer like raspberry pi.
6-I like the logo
7-Lazarus and FPC people are kind.Im still new to this word but until now they help me a lot and I appreciate that much.
I think if you want do company works do with Delphi but for personal,free,small,big projects choose Lazarus and FPC.
Delphi with it's very big components world is good for get jobs done but Lazarus and FPC are very good tools to make dreams real.
And don't forget these are my personal opinions