Well... Navionics charts for the most part are not surveyed but digitized/extrapolated from old topo maps and updated via crowd sourcing uploads...this is the SONARCharts part. The community edits are updates like new buoys, marinas, etc. which change constantly. Both are what you get for the $99 per year subscription...less than $10 per month. Garmin is out actually augmenting the Navionics data with scanning boats but I am not sure how massive an effort that might be but I understand they have been spotted in various places. Needless to say, Navionics data is currently the least accurate of all...at least until such time as the new data from the scanning boats gets integrated into the model.
Lakemaster changes as new lakes are actually surveyed and added to the card...which happens. Not sure what the triggering number of new lakes happens to be before a new version is released but that is the way they handle it as I understand it. To gain those updates, you purchase a new card.
C-Maps are basically the same as Lakemaster but with the option of updating. No details on the subscription costs at this time but it should be pretty reasonable. The updates will include fixes to existing lakes as well as adding potential new lakes in a state as they get scanned...the update process is still under development.
Lakes change but it is very rare that previously HD scanned lakes get rescanned...it simply costs too much to do so. So updates to existing HD scans simply are not going to happen often. It costs an amazing amount of money to scan a lake much less a whole state of tournament level lakes. It is not getting cheaper and the cost of mapping technology will continue to rise going forward. Some anglers, especially those that are focused on shallow water, will simply stay with whatever they have and not spend money. Serious offshore anglers live/die by the quality of the mapping and are willing to pay for it.
There are amazing things coming in the next few years but it isn't going to be something you can get for $99 per year... just saying...
You are certainly not required to buy anything...but you will be competing against those that will.