On top of what Matt already mentioned, most of the enterprise clients are going towards visualization tools that are more adaptive and responsive. Users want tools that look modern and can crossfilter when you click on charts.
SSRS has none of theose features and is very static. Also, there is a learning curve for developing reports in SSRS while in Power BI, you can make reports just by dragging and dropping. That said, SSRS still has it's space as there are some enterprise level features that are not available in Power BI yet (but I suspect that over time, Power BI is going to get a lot of those features).
I want to throw a couple ideas on here as well. Really SSRS is for your pixel perfect, operational reporting. Power BI is first and foremost an Analysis tool, it allows you to visualize your data in different ways in order to allow deeper understanding of your business.
The two tools really work together with SQL 2016, I encourage everyone to look into the new vision for BI going forward. SSRS reports in Power BI Service, Desktop files as backend for SSRS reports - looks really exciting.
we had requirement for some basic reporting work for one of our clients. they didn't had big IT team and had minimal budget to spend on the work. they had old source system which had firebird database. we had two options to propose them,
a. SSRS - requires them purchasing sql server licenses, define scope for requirements, developer to work on those requirements, consider deployment, schedule refresh of data from firebird using SSIS, static reports with BI developer needed to make changes
b. PowerBI - Free to use, works with unstructured data, user create their own reports by drag and drop of fields, minimal training required, modern rendering
only catch here was that with PowerBI data goes to the cloud while with SSRS it stays on premises but using DirectQuery is workaround.
Power BI is free... until you use any paying feature including workspaces for collaboration, content packs for publishing or gateway if you have no vpn to your databases. So virtually all you need for a professional deployment is a pro feature which means that from creating report to consuming dashboard, you will need a pro account.
Our issue is that our clients are government based and our software sits on there servers. Power bi requires them going out to the cloud which from government security view is undesirable. Plus it requires each user to have there own log in. One client has over 1000 users. I'd be interested in any advice from anyone who has faced this issue
Licensing is an issue - especially when it comes to cost.
The way we had the cloud issue resolved here in NZ, we had the local Cloud Suppliers go through a Government Security Vetting which verifies that their infrastructure/platform conforms to Military Grade security. That bypassed the issue regarding security.
As for licensing, because it may be prohibitive, some organisations have opted for more cost effective options thus using powerBI internally and other tech externally.
For use cases where the cloud is not an option, the on prem solution is Power BI publish to SSRS. It was developed for this exact scenario, as Power BI service sits in public Azure (no express route connection). As for having many users, you can add security groups or AD groups, so you don't have to manually add each user individually. This also applies for RLS set up in Power BI desktop.