That is fine for those who invest directly in shares. Brokers' commissions have fallen sharply, so active trading is not as expensive as it once was. But most private shareholders hold shares indirectly, through unit or investment trusts. Switching between funds is expensive. Nor is it easy to work out what is in your unit trust.
Most managers send out newsletters only twice a year - if at all.
While these will show the biggest holdings, that will not be enough to analyse strategy or performance. But that does not mean inertia rules for unit trust investors. You have to be just as careful about selecting a manager as you are about picking a share - and just as ruthless in deciding when to sell. In falling or turbulent markets there's no sense in being an index-tracker. At best they just follow the market down, but dealing costs mean performance will usually be worse than that.