It's to do with the operating systems Tilly et al. Part of Microsoft's vast income comes from the way adbots work and many software providers earn vast amounts of cash by piggybacking other software as part of their installation package, most are safe but if you don't want them they are a *** pest. Spam blockers and Virus filters do find them but it can take time a) to find them, b) to write the batch file that blocks it and issue updates.
Apple use non MS operating systems, Android is different again. Not many tablets use Microsoft.