You must renew your visa in your home country. There is a possibility of doing it in another country, such as Canada, but this is not usually recommended and has a higher probability of failing.
Mind you, these are people that already have visas. They are simply being renewed. The secondary effect of this is that it slows down processing of visas, which lowers how many are given out and increases the cost of the USCIS. Although I think this particular thing has existed for a while now, the Trump administration has made it a point to needlessly increase the processing time by making policies to delay the processing. This is a tactic that further slows down the USCIS, making it much more costly, just so that they can point out how costly and inefficient the USCIS is when it is their policies that make those things worse.
For example, if you make an application for an H-1B, extension, or renewal, it takes months to prepare the paperwork. Once submitted, the USCIS can send it back, requesting more information. This has become much more common under the Trump administration, because it basically adds a minimum three to six month delay to the process. It gets sent back to the applicant, one must extremely carefully understand the confusing request for more information, provide the information, and resubmit. The USCIS then starts the whole evaluation process back over again.