Universities generally are large and very bureaucratic institutions and making changes takes a great deal of time and administration.
As far as I am aware, there is no course where I work that can announce that in September they are going to change to, e.g. online only lectures, for reasons of pedagogic preference rather than national emergency.
They can't do this because to make that change they have to have their course revalidated to ensure it meets the standards required and the needs of the students.
To get the course revalidated they have to show there is student demand for this new way of teaching with actual evidence collected from students. They have to explain and justify why their proposed new methods are suitable, how they will meet the course aims and deliver appropriate learning outcomes, how they fit with university and national benchmarks and so on.
Once a course has produced their new proposal and completed the mountain of paperwork associated with it, it has to pass through scrutiny by a departmental committee, then a university committee and then another university committee composed of some of the most senior people in the university.
At each stage the proposal can be returned to the proposers with requests for change, or it can simply be rejected.
If everyone is not ridiculously busy with other things (which they are), it will take a month or two to gather evidence to complete the proposal documentation. If everyone really pulls out all the stops to get the proposal through it will take another couple of months to pass through the scrutiny committees. In practice at the moment it will probably take longer.
Only once all this is complete are the course and the university allowed to say 'this is how the course will be run'. This process has to be completed for both legal reasons and to maintain standards across the sector.
In normal times, which we hope to be in by September, it is very much not the case that an individual lecture or a whole university can just one day decide that they quite like teaching online and the next day announce to the world that this is what is going to happen from now on.