On .NET Framework you surely depend on OS integration, that is one of the major design changes in .NET Core.
Starting with Java 9, finally the long deprecated APIs started to be removed.
In any case, the issue is that we are forced to write C# 7 and Java 8 code.
Some well known examples, Sitecore, SharePoint WebParts, SQL Server SP extensions, Dynamics, Office AddIns, VS plugins, Solr extensions (many places keep using Solr on Java 8 even if more recent versions exist), Android (unless one goes Kotlin or targets version 12), Forms and WPF 3rd party components (the versions on .NET Core are incompatible due to new designer)...
Starting with Java 9, finally the long deprecated APIs started to be removed.
In any case, the issue is that we are forced to write C# 7 and Java 8 code.
Some well known examples, Sitecore, SharePoint WebParts, SQL Server SP extensions, Dynamics, Office AddIns, VS plugins, Solr extensions (many places keep using Solr on Java 8 even if more recent versions exist), Android (unless one goes Kotlin or targets version 12), Forms and WPF 3rd party components (the versions on .NET Core are incompatible due to new designer)...