The primary motivation to fork this project is enabling the support for .NET Standard. To make it possible, a lot of work was necessary and decisions must be taken.
The original project has some windows os specific behaviors like helpers to inject Windows Registry values directly as a dependency, RGB converters, and it address System.Drawing dependency. It just in Core, but Spring.NET has a lot of other projects, like Spring.Data, with abstractions to ADO Transaction Management and Unity Of Work with AOP, Spring.Data.NHibernate, with configurations about NHibernate, Spring.Services and children projects to support Enterprise Services, .NET Remoting, WCF and other technologies like AMQP.
All these things are cool but it's not necessary for me. All around spring.net is based on Spring.Core and Spring.AOP. All other projects mentioned above are based on this two projects. Many of my projects too.
To address this fork, without dependent customers, dependent community, I could make decisions, like remove windows specific dependencies, and reboot the project.
Before starting I tried to talk with the community that mantain the Spring.NET. You can see that in issues #133 and #144.