I worked in the mobile phone industry 00s. Besides terrible Series 60 UI, Symbian also had non-POSIX (micro?) kernel. For example, file system was a service and handles like a log file handle were not transferable across threads. It made porting apps a pain. Developer tools existed, but were shit and usual failure mode was app crashing without a reason.
Symbian had shitty developer experience because internally they did not have a "Dev experience and third party app development" stakeholder. They had kernel, seats for various hardware vendors, mobile and wifi standards, but not for third party devs. Nokia itself was blind for its mistakes as in-house they could get whatever source code or access they wanted.
Note that there were non-Symbian mobile phones as well e.g. Ericsson. So Symbian was kind of Android, but no default UI and closed source.
Symbian had shitty developer experience because internally they did not have a "Dev experience and third party app development" stakeholder. They had kernel, seats for various hardware vendors, mobile and wifi standards, but not for third party devs. Nokia itself was blind for its mistakes as in-house they could get whatever source code or access they wanted.
Note that there were non-Symbian mobile phones as well e.g. Ericsson. So Symbian was kind of Android, but no default UI and closed source.